Carbon based nonvolatile cross point memory incorporating carbon based diode select devices and MOSFET select devices for memory and logic applications

ABSTRACT

The present disclosure is directed toward carbon based diodes, carbon based resistive change memory elements, resistive change memory having resistive change memory elements and carbon based diodes, methods of making carbon based diodes, methods of making resistive change memory elements having carbon based diodes, and methods of making resistive change memory having resistive change memory elements having carbons based diodes. The carbon based diodes can be any suitable type of diode that can be formed using carbon allotropes, such as semiconducting single wall carbon nanotubes (s-SWCNT), semiconducting Buckminsterfullerenes (such as C60 Buckyballs), or semiconducting graphitic layers (layered graphene). The carbon based diodes can be pn junction diodes, Schottky diodes, other any other type of diode formed using a carbon allotrope. The carbon based diodes can be placed at any level of integration in a three dimensional (3D) electronic device such as integrated with components or wiring layers.

TECHNICAL FIELD

The present disclosure generally relates to carbon based nonvolatilecross point memory cells using carbon nanotubes, and other carbonallotropes, in corresponding memory arrays. It also relates to carbonbased diode select devices formed using carbon nanotubes and othercarbon allotropes, carbon based diodes formed as part of cross pointmemory cells, and carbon based diodes for use with any type ofelectronic device. It also relates to voltage scaled MOSFET selectdevices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to the following U.S. patents, which areassigned to the assignee of the present application, and are herebyincorporated by reference in their entirety:

-   -   U.S. Pat. No. 6,574,130, filed Jul. 25, 2001, entitled “Hybrid        Circuit Having Nanotube Electromechanical Memory;”    -   U.S. Pat. No. 6,643,165, filed Jul. 25, 2001, entitled        “Electromechanical Memory Having Cell Selection Circuitry        Constructed with Nanotube Technology;”    -   U.S. Pat. No. 6,706,402, filed Apr. 23, 2002, entitled “Nanotube        Films and Articles;”    -   U.S. Pat. No. 6,784,028, filed Dec. 28, 2001, entitled “Methods        of Making Electromechanical Three-Trace Junction Devices;”    -   U.S. Pat. No. 6,835,591, filed Dec. 28, 2001, entitled “Methods        of Making Electromechanical Three-Trace Junction Devices;”    -   U.S. Pat. No. 6,911,682, filed Dec. 28, 2001, entitled        “Electromechanical Three-Trace Junction Devices;”    -   U.S. Pat. No. 6,919,592, filed Jul. 25, 2001, entitled        “Electromechanical Memory Array Using Nanotube Ribbons and        Method for Making Same;”    -   U.S. Pat. No. 6,924,538, filed Feb. 11, 2004, entitled “Devices        Having Vertically-Disposed Nanofabric Articles and Methods of        Making the Same;”    -   U.S. Pat. No. 7,259,410, filed Feb. 11, 2004, entitled “Devices        Having Horizontally-Disposed Nanofabric Articles and Methods of        Making the Same;”    -   U.S. Pat. No. 7,335,395, filed Jan. 13, 2003, entitled “Methods        of Using Pre-Formed Nanotubes to Make Carbon Nanotube Films,        Layers, Fabrics, Ribbons, Elements and Articles;”    -   U.S. Pat. No. 7,375,369, filed Jun. 3, 2004, entitled        “Spin-Coatable Liquid for Formation of High Purity Nanotube        Films;”    -   U.S. Pat. No. 7,560,136, filed Jan. 13, 2003, entitled “Methods        of Using Thin Metal Layers to Make Carbon Nanotube Films,        Layers, Fabrics, Ribbons, Elements And Articles;”    -   U.S. Pat. No. 7,566,478, filed Jan. 13, 2003, entitled “Methods        of Making Carbon Nanotube Films, Layers, Fabrics, Ribbons,        Elements And Articles;”    -   U.S. Pat. No. 7,666,382, filed Dec. 15, 2005, entitled “Aqueous        Carbon Nanotube Applicator Liquids and Methods for Producing        Applicator Liquids Thereof;”    -   U.S. Pat. No. 7,745,810, filed Feb. 9, 2004, entitled “Nanotube        Films and Articles;”    -   U.S. Pat. No. 7,835,170, filed Aug. 8, 2007, entitled “Memory        Elements and Cross Point Switches and Arrays of Same Using        Nonvolatile Nanotube Blocks;”    -   U.S. Pat. No. 7,839,615, filed Jul. 27, 2009, entitled “Nanotube        ESD Protective Devices and Corresponding Nonvolatile and        Volatile Nanotube Switches;”    -   U.S. Pat. No. 7,852,114, filed Aug. 6, 2009, entitled        “Nonvolatile Nanotube Programmable Logic Devices and a        Nonvolatile Nanotube Field Programmable Gate Array Using Same;”    -   U.S. Pat. No. 7,928,523, filed Jul. 30, 2009, entitled        “Nonvolatile Electromechanical Field Effect Devices and Circuits        Using Same and Methods of Forming Same;”    -   U.S. Pat. No. 8,102,018, filed Aug. 8, 2007, entitled        “Nonvolatile Resistive Memories Having Scalable Two-Terminal        Nanotube Switches;”    -   U.S. Pat. No. 7,365,632, filed Sep. 20, 2005, entitled        “Resistive Elements using Carbon Nanotubes”;

This application is related to the following U.S. patent applications,which are assigned to the assignee of the present application, and arehereby incorporated by reference in their entirety:

-   -   U.S. patent application Ser. No. 11/835,852, filed Aug. 8, 2008,        entitled “Nonvolatile Nanotube Diodes and Arrays,” now U.S.        Patent Pub. No. 2008/0160734;    -   U.S. Patent App. No. 61/304,045, filed Feb. 12, 2012, entitled        “Methods for Controlling Density, Porosity, and/or Gap Size        within Nanotube Fabric Layers and Films;”    -   U.S. patent application Ser. No. 11/398,126, filed Apr. 5, 2005,        entitled “Nanotube Articles with Adjustable Electrical        Conductivity and Methods of Making the Same,” now U.S. Patent        Pub. No. 2006/0276065;    -   U.S. patent application Ser. No. 12/136,624, filed Jun. 10,        2008, entitled “Carbon Nanotube Films, Layers, Fabrics, Ribbons,        Elements and Articles,” now U.S. Patent Pub. No. 2009/0087630;    -   U.S. patent application Ser. No. 12/618,448, filed Nov. 13,        2009, entitled “A Method for Resetting a Resistive Change Memory        Element,” now U.S. Patent Pub. No. 2011/0038195;    -   U.S. patent application Ser. No. 13/076,152, filed Mar. 30,        2011, entitled “Methods for Arranging Nanotube Elements within        Nanotube Fabric and Films;”    -   U.S. patent application Ser. No. 12/874,501, filed Sep. 2, 2010,        entitled “Methods for Adjusting the Conductivity Range of a        Nanotube Fabric Layer;”    -   U.S. patent application Ser. No. 12/356,447, filed Jan. 20,        2009, entitled “Enhanced Memory Arrays and Programmable Logic        Circuit Operation and Manufacturability Using NV NT Switches        with Carbon Contacts and CNTs;”    -   U.S. patent application Ser. No. 12/066,053, filed Mar. 6, 2008,        entitled “Method and System of Using Nanotube Fabrics as Joule        Heating Elements for Memories and Other Applications,” now U.S.        Patent Pub. No. 2010/0327247;    -   U.S. Patent App. No. 61/074,241, filed on Jun. 20, 2008,        entitled “NRAM Arrays with Nanotube Blocks, Nanotube Traces, and        Nanotube Planes and Methods of Making Same”, now U.S. Patent        Pub. No. 2010/0001267;    -   U.S. Patent App. No. 61/319,034, filed on Mar. 30, 2010,        entitled “Methods of Reducing Gaps and Voids within Nanotube        Fabric Layers and Films.”

BACKGROUND OF THE INVENTION

A memory device is used by electronic devices to store data. Data storedin a memory device are represented by binary digit (bit) patterns formedfrom single bits, where each single bit has typically two possiblevalues: a logic 0 and a logic 1. The memory device stores the bitpatterns in memory elements that have different states corresponding todifferent possible values. For example, a two-state memory elementhaving a first state corresponding to a logic 0 and a second statecorresponding to a logic 1 can store a single bit. Some memory devicesare capable of storing more than two states, e.g., a four-state memoryelement having a first state corresponding to a logic 00, a second statecorresponding to a logic 01, a third state corresponding to a logic 10,and a fourth state corresponding to a logic 11 can store two bits. Ingeneral, an n-state memory element can store log₂ n bits, where log₂ nrefers to the binary logarithm of n.

The marketplace demand for low cost memory devices at lower costs withdata storage capacities has spurred the creation of memory devices withincreased memory densities. The traditional way of measuring memorydensity is the number of bits stored per square millimeter of layoutarea consumed (bits/mm²). Therefore, the memory density of a memorydevice can be increased by: reducing the feature sizes of memoryelements to consume less layout area, and increasing the number of bitsmemory elements can store. Vertically stacking memory layers to form athree-dimensional memory structure does not substantially increase thesize of the memory device or layout area because the vertical dimensionremains relatively small. Thus, bits/mm² remains a valid way ofmeasuring memory density. Two memory layers doubles the memory densityresulting in doubling the memory functionality in the approximately samelayout area.

Resistive change memory is a technology well suited to meet themarketplace demand for low cost memory devices with higher data storagecapacities. A resistive change memory device has resistive change memoryelements that are scalable to very high densities, incur very lowfabrication costs, store nonvolatile memory states, and consume verylittle power. Typically, the resistive change memory device stores databy adjusting the state of resistive change memory elements throughadjusting the state of a state-adjustable material between a number ofnonvolatile resistive states in response to applied stimuli. Forexample, a two-state resistive change memory element can be configuredto switch between a first resistive state (e.g., a high resistive state)that corresponds to a logic 0 and a second resistive state (e.g., a lowresistive state) that corresponds to a logic 1. Using these tworesistive states, the two-state resistive change memory element canstore a single bit. Similarly, a four-state resistive change memoryelement can be configured to switch between a first resistive state(e.g., a very high resistive state) that corresponds to a logic 00, asecond resistive state (e.g., a moderately high resistive state) thatcorresponds to a logic 01, a third resistive state (e.g., a moderatelylow resistive state) that corresponds to a logic 10, and a fourthresistive state (e.g., a very low resistive state) that corresponds to alogic 11. Using these four resistive states, the four-state resistivechange memory element can store two bits.

The electrically programmable read-only memory (EPROM) device disclosedby Roesner in U.S. Pat. No. 4,442,507 is a type of resistive changememory having two-state resistive change memory elements with thetwo-state resistive change memory elements having resistive materials ina series connection with Schottky diodes. The EPROM device stores datain the two-state resistive change memory elements by adjusting aresistance state of the resistive materials. Prior art FIG. 1 generallycorresponds to FIG. 11 of U.S. Pat. No. 4,442,507 and prior art FIG. 1illustrates a two-state resistive change memory element 10 formed by aresistive material 50 in a series connection with a Schottky diode 52.The resistive material 50 consists essentially of a single elementsemiconductor selected from the group of Si, Ge, C, and α-Sn, and isdeposited as a layer of 2,000 Å thickness. The resistive material 50 hasa high resistance state on the order of 10⁷ ohms before an electricalstimulus is applied and a low resistance state on the order of 10² ohmsafter the electrical stimulus is applied.

During a write operation the EPROM device adjusts the resistance stateof the two-state resistive change memory element 10 by supplying anelectrical stimulus in the form of a programming voltage above a desiredthreshold voltage to the two-state resistive change memory element 10.The application of the programming voltage causes the resistive material50 to irreversibly switch from the high resistance state to the lowresistance state. During a read operation the EPROM device senses theresistance state of the two-state resistive change memory element 10 bysupplying a preselected voltage and current to the two-state resistivechange memory element 10. The preselected voltage is limited to apreselected value below the desired threshold voltage for switching theresistance state of the resistive material 50 and the resulting currentare limited to below a preselected value. The high resistance state andthe low resistance state of the resistive material 50 produce differentvoltages across and different currents flowing through the two-stateresistive change memory element 10 in response to the EPROM devicesupplying the preselected voltage and current. Roesner provides theexemplary voltage across and current flowing through the two-stateresistive change memory element 10 with the resistive material 50 in thehigh resistance state of 5 V and 0.2 μA respectively, and the exemplaryvoltage across and the current flowing through the two-state resistivechange memory element 10 with the resistive material 50 in the lowresistance state of 0.25 V and 50 μA respectively. The differentvoltages and currents sensed by the EPROM device are interpreted as datastored in the two-state resistive change memory element 10.Additionally, the resistive change memory element 10 is non-volatilebecause power is not required to maintain the different resistancestates of the resistive material 50, and thus, the data is retained inthe two-state resistive change memory element 10 when power is removed.

In operation, the EPROM device disclosed by Roesner is formed with aSchottky diode and a nonvolatile programmable resistor in a relativelyhigh resistance initial state as fabricated. Decode circuits andSchottky diodes in each cell may be used to selectively causenonvolatile programmable resistor values to transition to a relativelylow resistance permanent state. That is, the EPROM-EROM is aone-time-programmable (OTP) memory. After the programming operation iscompleted, the EPROM device operates as a read-only memory.

The two-state resistive change memory element 10 illustrated in priorart FIG. 1 is fabricated on an insulating layer 12 of SiO₂ that isdeposited over a semiconductor substrate 11 containing circuitry for theEPROM device. The insulating layer 12 is 7,000 Å-10,000 Å thick tosmooth out surface 12 a and also to minimize any capacitances betweenthe two-state resistive change memory element 10 and the underlyingcircuitry for the EPROM device. The two-state resistive change memoryelement 10 is constructed from a semiconductor lead 14, an insulator 16,the Schottky diode 52, the resistive material 50, and a metal lead 20.

The semiconductor lead 14 has a polycrystalline layer of N+semiconductor material deposited on the surface 12 a of the insulatinglayer 12 and a polycrystalline layer of N− semiconductor materialdeposited on the polycrystalline layer of N+ semiconductor material. Thepolycrystalline layer of N+ semiconductor material and thepolycrystalline layer of N− semiconductor material are fabricated bydepositing either silicon or germanium and then doping the silicon orthe germanium in-situ. The polycrystalline layer of N+ semiconductormaterial has a dopant atom concentration of at least 10²⁰ atoms/cm³ andthe polycrystalline layer of N− semiconductor material has a dopant atomconcentration of 10¹⁴-10¹⁷ atoms/cm³ with arsenic, phosphorous, andantimony being suitable dopant impurity atoms for both polycrystallinelayers. The insulator 16 is then formed by depositing a layer of SiO₂over the surface 12 a and the semiconductor lead 14 with subsequentmasking and etching of the insulator 16 to form a contact hole over thesemiconductor lead 14. Thereafter, the semiconductor lead 14 and theinsulator 16 are annealed at 900° C. to increase the crystalline grainsize of both polycrystalline layers in semiconductor lead 14 and to movethe dopant atoms from interstitial to substitutional positions in thelattice network of both polycrystalline layers in the semiconductor lead14.

The Schottky diode 52 has a cathode formed by the polycrystalline layerof N-semiconductor material of the semiconductor lead 14 and an anodeformed by a platinum compound (e.g. platinum silicide) 18. The Schottkydiode 52 is fabricated by depositing a layer of platinum on the exposedportion of the polycrystalline layer of N− semiconductor material andheating the layer of platinum to 450° C. to form the platinum compound(e.g. platinum silicide) 18 with the polycrystalline layer of N−semiconductor material. The resistive material 50 is then deposited onthe platinum compound with special care taken throughout the fabricationprocess to prevent the resistive material 50 from being exposed totemperatures greater than 600° C. This temperature constraint is imposedon the fabrication process to ensure that the crystalline grain size ofthe resistive material 50 is substantially smaller than the crystallinegrain size of the polycrystalline layer of N-semiconductor material ofthe semiconductor lead 14 and also to ensure that any dopant atoms inthe resistive material 50 are interstitial in the lattice instead ofsubstitutional. Additionally, the amount of current required forresistive material 50 to switch resistance states is dependent on themaximum temperature that the resistive material 50 is exposed to withthe amount of current required for the resistive material 50 to switchresistance states increasing in a highly nonlinear manner as the maximumtemperature increases. Roesner provides the example of when theresistive material 50 is processed at a maximum temperature of 600° C.the resistive material 50 might require only 10 μA to switch resistivestates and when the resistive material 50 is processed at a maximumtemperature of 750° C. the resistive material 50 might require severalmilliamps to switch resistance states.

The metal lead 20 has a bottom layer 22 formed by a barrier metal and atop layer 24 formed by a conductive metal. The barrier metal preventsthe conductive metal from migrating into the resistive material 50. Themetal lead 20 is fabricated by depositing the bottom layer 22 oftitanium tungsten on the resistive material 50 and the top layer 24 ofaluminum on the bottom layer of titanium tungsten.

SUMMARY OF THE DISCLOSURE

The present disclosure relates to carbon based nonvolatile cross pointmemory incorporating carbon based diode select devices and MOSFET selectdevices for memory and logic applications.

In particular, the present disclosure discloses a diode. In particular,the diode comprises a first carbon layer and a second carbon layer inelectrical communication with the first carbon layer, wherein the firstcarbon layer and the second carbon layer are configured to create aconductive path when sufficient voltage is applied. Under one aspect ofthe present disclosure, at least one of the first carbon layer and thesecond carbon layer is a nanotube fabric layer. Under another aspect ofthe present disclosure, at least one of the first carbon layer and thesecond carbon layer is a graphitic layer. Under yet another aspect ofthe present disclosure, at least one of the first carbon layer and thesecond carbon layer is a buckyball layer.

The present disclosure also discloses a resistive change element. Inparticular, the resistive change element comprises a nonvolatileresistive block switch, wherein the nonvolatile resistive block switchcomprises a first metal layer and a switch carbon layer in electricalcommunication with the first metal layer. The resistive change elementfurther comprises a diode in a series connection with the nonvolatileresistive block switch, wherein the diode comprises a first diode carbonlayer and a second diode carbon layer in electrical communication withthe first diode carbon layer, wherein the first diode carbon layer andthe second diode carbon layer are configured to create a conductive pathwhen sufficient voltage is applied. Under one aspect of the presentdisclosure, the switch carbon layer is at least one of a switch nanotubefabric layer, a switch graphitic layer, and a switch buckyball layer.Under another aspect of the present disclosure, the diode carbon layeris at least one of a diode nanotube fabric layer, a diode graphiticfabric layer, and a diode buckyball layer. Under yet another aspect ofthe present disclosure, the resistive change element is a resistivechange memory element. Under still yet another aspect of the presentdisclosure, the resistive change element is a resistive change logicelement.

The present disclosure also discloses a vertical resistive change array.In particular, the vertical resistive change array comprises verticalcolumn element and at least one storage bit plane, wherein at least onestorage bit plane comprises at least one resistive change element, inelectrical communication the vertical column element. Under one aspectof the present disclosure, the resistive change element comprises atleast a carbon layer and said carbon layer is at least one of a nanotubefabric layer, a graphitic layer, and a buckyball layer. Under anotheraspect of the present disclosure, the resistive change element is aresistive change memory element. Under yet another aspect of the presentdisclosure, the resistive change element is a resistive change logicelement.

Other features and advantages of the present disclosure will becomeapparent from the description and drawings provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1, prior art, illustrates a two-state resistive change memoryelement formed by a resistive material in a series connection with aSchottky diode.

FIG. 1A illustrates an NRAM memory cell formed with a select device anda resistive nonvolatile memory element;

FIGS. 1B-1, 1B-2, and 1B-3 illustrate a two-terminal cross point array;

FIG. 1C illustrates a NV CNT resistive change memory cell formed with aswitch nanotube block and top and bottom conductive terminals;

FIG. 1D illustrates a NV graphitic resistive change memory cell formedwith a switch graphic block and top and bottom conductive terminals;

FIG. 1E illustrates a NV buckyball resistive change memory cell formedwith a switch buckyball block and top and bottom conductive terminals;

FIG. 2A illustrates a representation of a cross point array in a READmode that shows selected current and parasitic current flows in crosspoint cells, referred to as resistive 1-R cells;

FIG. 2B illustrates a graph of cross point array requirements in termsof the number of cells as a function of the minimum ON-state resistancevalue of a nonvolatile nonlinear resistive storage element;

FIG. 3A illustrates an I-V curve of a NV CNT resistive block switch withan ON-state resistance of 1 mega-Ohm;

FIG. 3B illustrates a graph of cross point array requirements in termsof the number of cells in a cross point switch array for a NV CNTresistive block switch with an ON-state resistance of 1 mega-Ohm;

FIG. 3C illustrates ON-state and OFF-state resistance values for NV CNTresistive block switches;

FIG. 3D illustrates an SEM of a NV CNT resistive switch formed with asquare switch nanotube block having dimensions of 15 nm;

FIG. 3E illustrates the NV CNT resistive switch of FIG. 3D in operation;

FIG. 4A illustrates a resistive change memory element formed by anonvolatile CNT resistive block switch, an interposed conductive layer,and a carbon based diode configured as a Schottky diode having aconductive layer electrically contacting a diode nanotube fabric layer;

FIG. 4B illustrates an alternative embodiment of a resistive changememory element formed by a nonvolatile CNT resistive block switch and acarbon based diode configured as a Schottky diode having a conductivelayer electrically contacting a diode nanotube fabric layer;

FIG. 4C illustrates an ion implantation device for in situ doping of atarget material by ion implantation;

FIG. 4D illustrates ion implantation of a nanotube fabric layer with anangle of incidence of ion beams being a direct angle;

FIG. 4E illustrates ion implantation of a nanotube fabric layer with anangle of incidence of ion beams being greater than zero degrees;

FIG. 4F illustrates a carbon based diode configured as a Schottky diodehaving a conductive layer electrically contacting a p-type diodenanotube fabric layer;

FIG. 4G illustrates a carbon based diode configured as a Schottky diodehaving a conductive layer electrically contacting an n-type diodenanotube fabric layer;

FIG. 4H illustrates a carbon based diode configured as a pn junctiondiode having a p-type diode nanotube fabric layer electricallycontacting an n-type diode nanotube fabric layer;

FIG. 5A illustrates a resistive change memory element formed by anonvolatile CNT resistive block switch, an interposed conductive layer,and a carbon based diode configured as a Schottky diode having aconductive layer electrically contacting a diode graphitic layer;

FIG. 5B illustrates an alternative embodiment of a resistive changememory element formed by a nonvolatile CNT resistive block switch and acarbon based diode configured as a Schottky diode having a conductivelayer electrically contacting a diode graphitic layer;

FIG. 5C illustrates a resistive change memory element formed by anonvolatile graphitic resistive block switch, an interposed conductivelayer, and a carbon based diode configured as a Schottky diode having aconductive layer electrically contacting a diode graphitic layer;

FIG. 5D illustrates an alternative embodiment of a resistive changememory element formed by a nonvolatile graphitic resistive block switchand a carbon based diode configured as a Schottky diode having aconductive layer electrically contacting a diode graphitic layer;

FIG. 5E illustrates a carbon based diode configured as a Schottky diodehaving a conductive layer electrically contacting a p-type diodegraphitic layer;

FIG. 5F illustrates a carbon based diode configured as a Schottky diodehaving a conductive layer electrically contacting an n-type diodegraphitic layer;

FIG. 5G illustrates a carbon based diode configured as a pn junctiondiode having a p-type diode graphitic layer electrically contacting ann-type diode graphitic layer;

FIG. 6A illustrates a resistive change memory element formed by anonvolatile CNT resistive block switch, an interposed conductive layer,and a carbon based diode configured as a Schottky diode having aconductive layer electrically contacting a diode buckyball layer;

FIG. 6B illustrates an alternative embodiment of a resistive changememory element formed by a nonvolatile CNT resistive block switch and acarbon based diode configured as a Schottky diode having a conductivelayer electrically contacting a diode buckyball layer;

FIG. 6C illustrates a resistive change memory element formed by anonvolatile buckyball resistive block switch, an interposed conductivelayer, and a carbon based diode configured as a Schottky diode having aconductive layer electrically contacting a diode buckyball layer;

FIG. 6D illustrates an alternative embodiment of a resistive changememory element formed by a nonvolatile buckyball resistive block switchand a carbon based diode configured as a Schottky diode having aconductive layer electrically contacting a diode buckyball layer;

FIG. 6E illustrates a carbon based diode configured as a Schottky diodehaving a conductive layer electrically contacting a p-type diodebuckyball layer;

FIG. 6F illustrates a carbon based diode configured as a Schottky diodehaving a conductive layer electrically contacting an n-type diodebuckyball layer;

FIG. 6G illustrates a carbon based diode configured as a pn junctiondiode having a p-type diode buckyball layer electrically contacting ann-type diode buckyball layer;

FIG. 7A illustrates a resistive change memory element in a high densitycross-point array configuration, where the resistive change memoryelement is formed by a nonvolatile CNT resistive block switch and acarbon based diode configured as a Schottky diode having a conductivelayer electrically contacting a diode nanotube fabric layer;

FIG. 7B illustrates a resistive change memory element in a high densitycross-point array configuration, where the resistive change memoryelement is formed by a nonvolatile CNT resistive block switch and acarbon based diode configured as a Schottky diode having a conductivelayer electrically contacting a diode graphitic layer;

FIG. 7C illustrates a resistive change memory element in a high densitycross-point array configuration, where the resistive change memoryelement is formed by a nonvolatile CNT resistive block switch and acarbon based diode configured as a Schottky diode having a conductivelayer electrically contacting a diode buckyball layer;

FIG. 8A illustrates an example of a process flow for fabricatingresistive change memory elements in a high density cross-point array;

FIG. 8B illustrates a starting wafer having a smooth surface afterchemical mechanical planarization;

FIG. 8C illustrates a diode nanotube fabric layer, a first metal layer,a switch nanotube fabric layer, and a second metal layer deposited on asmooth surface of a starting wafer;

FIG. 8D illustrates patterned and etched stacks that form a first diodenanotube fabric layer, a second diode nanotube fabric layer, a firstbottom metal layer, a second bottom metal layer, a first switch nanotubefabric layer, a second switch nanotube fabric layer, a first top metallayer, and a second top metal layer;

FIG. 8E illustrates a dielectric fill for sidewall passivation ofpatterned and etched stacks and a dielectric fill between the patternedand etched stacks;

FIG. 8F illustrates a single-level nonvolatile resistive change memoryhaving two resistive change memory elements fabricated in a high densitycross-point array;

FIG. 9A illustrates a single-level nonvolatile resistive change memoryhaving two resistive change memory elements fabricated in a high densitycross-point array with a thick dielectric layer, a third top metallayer, and a fourth top metal layer deposited and planarized on top ofthe single-level nonvolatile resistive change memory;

FIG. 9B illustrates a multi-level nonvolatile resistive change memoryhaving resistive change memory elements formed by nonvolatile CNTresistive block switches and carbon based diodes configured as Schottkydiodes having conductive layers electrically contacting diode nanotubefabric layers;

FIG. 10A illustrates a single-level nonvolatile resistive change memoryhaving two resistive change memory elements fabricated in a high densitycross-point array using a graphitic layer;

FIG. 10B illustrates a multi-level nonvolatile resistive change memoryhaving vertically stacked resistive change memory elements formed bynonvolatile CNT resistive block switches and carbon based diodesconfigured as Schottky diodes having conductive layers electricallycontacting diode graphitic layers;

FIG. 11A illustrates a single-level nonvolatile resistive change memoryhaving two resistive change memory elements fabricated in a high densitycross-point array using a buckyball layer;

FIG. 11B illustrates a multi-level nonvolatile resistive change memoryhaving vertically stacked resistive change memory elements formed bynonvolatile CNT resistive block switches and carbon based diodesconfigured as Schottky diodes having conductive layers electricallycontacting diode buckyball layers;

FIG. 12A illustrates a scanning electron microscope (SEM) image of anunordered nanotube fabric;

FIG. 12B illustrates a scanning electron microscope (SEM) image of anordered nanotube fabric;

FIGS. 13A, 13B, 13C, 13D, and 13E illustrate a cross point memory arraywith vertical columns of array line segments;

FIG. 14 illustrates a discrete two-terminal nonvolatile nanotube switchwith end contacts;

FIG. 15 illustrates the measured electrical behavior of the nonvolatilenanotube switch of FIG. 14;

FIGS. 16A and 16B illustrate methods of fabrication for making the crosspoint array structure of FIGS. 13A-13E;

FIGS. 17A-17I illustrates cross sections corresponding to the methods offabrication of FIGS. 16A and 16B

FIG. 18 illustrates expected nonvolatile random access memory capacityand nanosecond speed requirements for the 15 nm and sub-15 nm technologynodes;

FIG. 19 illustrates measured 4 Mb NRAM memory chip electricalperformance characteristics;

FIG. 20 illustrates a schematic representation of CNT switchcharacteristic illustrating the inherently high speed switching ofcarbon nanotube fabrics;

FIG. 21 illustrates a block diagram representation of a cross pointmemory array and corresponding sub-arrays;

FIG. 22 illustrates a cross sectional representation of array wires inthe sub-arrays of FIG. 21;

FIGS. 23A, 23B, and 23C illustrate a cross point array formed with acell having enhanced select characteristics, referred to as enhancedselectivity resistive 1-RS cells;

FIGS. 24A, 24B, and 24C illustrate cross sections of structures formedas a result of fabrication methods that may be used to form switchnanotube blocks using regions of conductive CNT fabrics and regions ofnonconductive CNT fabrics to isolate switch nanotube blocks fromadjacent cells in cross point memory arrays;

FIGS. 25 and 26 illustrate images from a field emission scanningelectron microscope (FESEM) showing the results of experiments used todemonstrate methods of converting regions (portions) of CNT fabrics fromconductive to nonconductive, while leaving conductive regions intact;

FIGS. 27A, 27B, 28A, 28B, 29 and 30 illustrate the application of thestructures and corresponding methods of fabrication described withrespect to FIGS. 24-26 using top contacts as masks for exposingnon-protected CNT fabric regions to plasma or ion implantation to formcross point arrays with nonconductive or high resistance CNT fabrics toisolate cells in cross point arrays;

FIG. 31 illustrates the use of conductive and nonconductive graphiticlayers using top contacts as masks to form cross point arrays withnonconductive or high-resistance graphitic layers to isolate cells incross point arrays; and

FIG. 32 illustrates the use of conductive and nonconductive buckyballlayers using top contacts as masks to form cross point arrays withnonconductive or high-resistance buckyball layers to isolate cells incross point arrays.

FIGS. 33A, 33B, and 33C illustrate methods of fabrication for making thecross point array structure of FIG. 21;

FIGS. 34A, 34B illustrate a plan view and cross section, respectively,of bottom array wires embedded in dielectric on a substrate;

FIG. 34C illustrates a plan view of top array wires on a contact layer.The contact layer is deposited on a CNT fabric layer;

FIG. 34D-1 illustrates a cross section, corresponding to FIG. 34C,including a CNT fabric layer on the surface of FIG. 34B with a top arraywires formed on a contact layer between the top array wires and the CNTfabric layer;

FIG. 34D-2 illustrates a cross section similar to FIG. 34D-1, exceptthat the CNT fabric layer includes a switch nanotube fabric layerintegrated with a diode nanotube fabric layer;

FIG. 34D-3 illustrates a cross section showing a variation of the CNTfabric layer shown in FIG. 34D-2;

FIG. 34E illustrates a cross section that shows a first ion implantbetween top array wires that penetrates through the exposed contactlayer into the CNT fabric layer. Prior to ion implantation, the entireCNT fabric layer is a CNT switching region. The first ion implantchanges the CNT fabric region between top array wires intohigh-resistance isolation regions self-aligned to top array wires;

FIG. 34F illustrates a cross section corresponding to FIG. 34E thatshows the CNT fabric region after the first ion implant step. CNT fabricregions under the top array wires remain CNT switching regions, whileCNT fabric regions between top array wires are converted tohigh-resistance isolation regions;

FIG. 34G illustrates the cross section shown in FIG. 34F after theformation of a first sacrificial layer;

FIG. 35A illustrates a plan view of sacrificial array masking wires,parallel to underlying bottom array wires, formed on the surface of FIG.34G;

FIG. 35B illustrates a plan view of FIG. 35A after exposed regions oftop array wires have been removed (etched) revealing contact layerregions. Top array wires are segmented;

FIG. 35C illustrates a cross section of FIG. 35B through the length ofsacrificial array masking wire;

FIG. 35D illustrates a cross section of FIG. 35B between sacrificialarray masking wires and parallel to the sacrificial array masking wires;

FIG. 35E illustrates a cross section of FIG. 35B through the entire FIG.35B structure, orthogonal to the sacrificial array masking wires,through top array wire segments, and through the length of the bottomarray wires;

FIG. 35F illustrates a cross section of FIG. 35B through the entire FIG.35B structure orthogonal to the sacrificial array masking wires andbetween top array wires segments;

FIG. 36A illustrates a cross section of a second ion implant applied tothe cross section shown in FIG. 35C;

FIG. 36B illustrates the cross section of FIG. 35C after the second ionimplant step, and shows that the ion implant was blocked from CNT fabriclayer, leaving CNT switching regions unchanged;

FIG. 36C illustrates a cross section of a second ion implant applied tothe cross section shown in FIG. 35D;

FIG. 36D illustrates the cross section of FIG. 35D after the second ionimplant step has converted exposed CNT fabric regions to high-resistanceisolation regions;

FIG. 36E illustrates a cross section of a second ion implant applied tothe cross section shown in FIG. 35E;

FIG. 36F illustrates the cross section of FIG. 35E after the second ionimplant step has converted exposed CNT fabric regions to high-resistanceisolation regions;

FIG. 37A: illustrates a plan view of FIG. 35B after sacrificial arraymasking wires have been removed;

FIG. 37B illustrates a cross section of plan view 37B through segmentedtop array wires;

FIG. 37C illustrates cross section 37B after damascene conductordeposition and planarization re-connects top array wires segments tore-form top array lines;

FIG. 37D illustrates a plan view corresponding to cross section 37Bshowing reformed top array wires;

FIG. 37E illustrates a plan view corresponding to plan view 37D afterthe exposed contact layer between top array wires has been removed(etched);

FIG. 38A illustrates plan a plan view corresponding to plan view 37Eafter deposition and planarization of a protective insulator;

FIG. 38B illustrates a cross section of FIG. 38A through the entirestructure and through a bottom array wire. The cross section showsintegrated nonvolatile CNT resistive blocks switches with CNT switchingregions of minimum dimension F, defined by the intersection of arraywires, along the length of the underlying bottom array wire andhigh-resistance isolation regions between the switches;

FIG. 38C illustrates a cross section of FIG. 38A through the entirestructure and through a top array wire. The cross section showsintegrated nonvolatile CNT resistive blocks switches with CNT switchingregions of minimum dimension F, defined by the intersection of arraywires, along the length of the overlying top array wire withhigh-resistance isolation regions between the switches;

FIG. 38D illustrates a cross section of FIG. 38A orthogonal to top arraywires between CNT switching regions showing high-resistance isolationregions in the CNT fabric layer between the top array wires;

FIG. 38E illustrates a cross section of FIG. 38A orthogonal to bottomarray wires between CNT switching regions showing high-resistanceisolation regions in the CNT fabric layer between the bottom arraywires;

FIG. 39 illustrates a cross section in which sacrificial top markingwires are misaligned with respect to bottom array wires to showintegrated nonvolatile CNT resistive block switch insensitivity to thealignment; CNT switching regions of minimum dimension F are also definedby the intersection of array wires;

FIG. 40 illustrates a cross point array used to interconnect top andbottom wires for purposes of signal routing, voltage distribution,and/or power distribution. All NV CNT resistive block switches are in ahigh resistance RESET state;

FIGS. 41A, 41B, 41C, and 41D illustrate the cross point array of FIG. 40in which selected NV CNT resistive block switches are in a lowresistance SET state;

FIG. 42 illustrates a cross point array-based programmable array logicfunction;

FIGS. 43A and 43B illustrate diode-resistor logic circuits;

FIG. 44 illustrates a field programmable gate array;

FIGS. 45A, 45B, 45C, and 45D illustrate various configurable routing andlogic circuits;

FIG. 46 illustrates a configurable logic block formed with configurablecombinatorial logic circuits;

FIG. 47 illustrates a configurable logic block formed with alook-up-table (LUT) using a cross point array;

FIG. 48 illustrates a protective device circuit;

FIG. 49 illustrates a nonvolatile resistive memory sub-array schematicusing a first architecture;

FIGS. 50A, 50B, 50C, and 50D illustrate first architecture modes ofoperation for the sub-array of FIG. 59;

FIG. 51 illustrates a nonvolatile resistive memory sub-array schematicusing a second architecture;

FIGS. 52A, 52B, 52C, and 52D illustrate second architecture modes ofoperation for the sub-array of FIG. 51;

FIGS. 53, 54A, and 54B tables summarize first and second architectureoperating conditions for mode 1;

FIGS. 55, 56A, and 56B tables summarize first and second architectureoperating conditions for mode 2;

FIG. 57 table summarizes MOSFET scaled voltage requirements as afunction of first and second architectures and operating modes 1 and 2.

DETAILED DESCRIPTION NRAM and Cross Point Memory Cells

The present disclosure is generally directed toward nonvolatileresistive change memory cells (or elements) forming 1-R memory cells ina cross point cell configuration, approximately 4F² in area, with cellselect and nonvolatile storage functions combined in a single element.Nonvolatile resistive change memory elements using carbon layers asstorage elements can form cross point nonvolatile resistive memoryelements. In the present disclosure, the term carbon layer is defined asany allotrope of carbon, excluding amorphous carbon.

To elaborate further, a carbon layer as referred to herein for thepresent disclosure includes a layer of multiple, interconnected carbonstructures (such as, but not limited to, carbon nanotubes, graphite,buckyballs, and nanocapsules) formed in a layer such as to provide atleast one electrically conductive path through the layer. The carbonlayer can be, for example, a nanotube fabric (as described in detailbelow). Further, in another example, this carbon layer can be one ormore sheets of graphene (or graphitic layer). In yet another example,the carbon layer can be a deposition of carbon fullerenes (such as, butnot limited to, carbon buckyballs or elongated nanocapsules).

In the present disclosure, carbon layers can be used to form diodecarbon layers, such as, for example, diode nanotube fabric layers, diodegraphitic layers, or diode buckyball layers. In the present disclosure,the term diode nanotube fabric layer refers to one or more nanotubefabric layers acting as, or as part of, a diode (as described in detailbelow). For example, a nanotube fabric layer in contact with a metallayer to form a Schottky diode. Or, for example, a p-type nanotubefabric layer in contact with an n-type nanotube fabric layer to form apn diode. The term diode graphitic layer refers to one or more graphiticlayers acting as, or as part of, a diode (as described in detail below).The term diode buckyball layer refers to one or more buckyball layersacting as, or as part of, a diode (as described in detail below).

In certain applications this carbon layer is patterned (via, forexample, photolithography and etch) such that the layer of multiple,interconnected carbon structures conforms to a preselected geometry.Further, the carbon layer can be deposited or formed (via, for example,a spin coating operation of the individual structures) to have apreselected thickness, density, and/or porosity. The carbon layer can beordered (wherein the individual carbon structures are substantiallyoriented in a uniform direction) or unordered (wherein the individualcarbon structures are oriented independently of adjacent structures).

Carbon layers can be patterned into structures referred to as blocks inthe present disclosure. For example, FIG. 1C shows a NV CNT resistivechange memory cell formed with a switch nanotube block and top andbottom conductive terminals. In another example, FIG. 13A shows a NV CNTresistive change memory cell formed with a switch nanotube block and endcontacts to conductive terminals (in this example, array lines). In atleast one embodiment, this block is a nanotube fabric block.

Relatively high ON-state (R_(ON)) minimum resistance values, in themega-Ohm range for example, and OFF-state resistance (R_(OFF)) toON-state resistance ratios R_(OFF)/R_(ON) in excess of 2, are needed toachieve arrays of sufficient size as described in J. Liang et al.,“Cross-Point Memory Array Without Cell Selectors—Device Characteristicsand Data Storage Pattern Dependencies”, IEEE Transactions on ElectronDevices, Vol. 57, No. 10, October 2010. In summary, 1-R memory cells ina cross point cell configuration require high R_(ON) values and a highdegree of nonlinearity when comparing R_(ON) and R_(OFF) values toexhibit sufficient select and nonvolatile storage element behavior.

A fabric of nanotubes as referred to herein for the present disclosureincludes a layer of multiple, interconnected carbon nanotubes. A fabricof nanotubes (or nanofabric), in the present disclosure, e.g., anon-woven carbon nanotube (CNT) fabric, may, for example, have astructure of multiple entangled nanotubes that are irregularly arrangedrelative to one another. Alternatively, or in addition, for example, thefabric of nanotubes for the present disclosure may possess some degreeof positional regularity of the nanotubes, e.g., some degree ofparallelism along their long axes. Such positional regularity may befound, for example, on a relatively small scale wherein flat arrays ofnanotubes are arranged together along their long axes in rafts on theorder of one nanotube long and ten to twenty nanotubes wide. In otherexamples, such positional regularity maybe found on a larger scale, withregions of ordered nanotubes, in some cases, extended over substantiallythe entire fabric layer. Such larger scale positional regularity is ofparticular interest to the present disclosure.

The fabrics of nanotubes retain desirable physical properties of thenanotubes from which they are formed. For example, in some electricalapplications the fabric preferably has a sufficient amount of nanotubesin contact so that at least one ohmic (metallic) or semi-conductivepathway exists from a given point within the fabric to another pointwithin the fabric. Single wall nanotubes may typically have a diameterof about 1-3 nm, and multi-wall nanotubes may typically have a diameterof about 3-30 nm. Nanotubes may have lengths ranging from about 0.2microns to about 200 microns, for example. The nanotubes may curve andoccasionally cross one another. Gaps in the fabric, i.e., betweennanotubes either laterally or vertically, may exist. Such fabrics mayinclude single wall nanotubes, multi-wall nanotubes, or both. The fabricmay have small areas of discontinuity with no tubes present. The fabricmay be prepared as a layer or as multiple fabric layers, one formed overanother. The thickness of the fabric can be chosen as thin assubstantially a monolayer of nanotubes or can be chosen much thicker,e.g., tens of nanometers to tens of microns in thickness. The porosityof the fabrics can vary from low density fabrics with high porosity tohigh density fabrics with low porosity. Such fabrics can be prepared bygrowing nanotubes using chemical vapor deposition (CVD) processes inconjunction with various catalysts, for example. Other methods forgenerating such fabrics may involve using spin-coating techniques andspray-coating techniques with preformed nanotubes suspended in asuitable solvent, silk screen printing, gravure printing, andelectrostatic spray coating. Nanoparticles of other materials can bemixed with suspensions of nanotubes in such solvents and deposited byspin coating and spray coating to form fabrics with nanoparticlesdispersed among the nanotubes. Such exemplary methods are described inmore detail in the related art cited in the Background section of thisdisclosure.

As described within U.S. Pat. No. 7,375,369 and U.S. Pat. No. 7,666,382,both incorporated herein by reference in their entirety, nanotubefabrics and films can be formed by applying a nanotube applicationsolution (for example, but not limited to, a plurality of nanotubeelements suspended within an aqueous solution) over a substrate element.A spin coating process, for example, can be used to evenly distributethe nanotube elements over the substrate element, creating asubstantially uniform layer of nanotube elements. In other cases, otherprocesses (such as, but not limited to, spray coating processes, dipcoating processes, silk screen printing processes, and gravure printingprocesses) can be used to apply and distribute the nanotube elementsover the substrate element. In other cases, CVD growth of nanotubes on amaterial surface may be used to realize an unordered nanotube fabriclayer. Further, U.S. Patent App. No. 61/304,045, incorporated herein byreference in its entirety, teaches methods of adjusting certainparameters (for example, the nanotube density or the concentrations ofcertain ionic species) within nanotube application solutions to eitherpromote or discourage rafting—that is, the tendency for nanotubeelements to group together along their sidewalls and form dense,raft-like structures—within a nanotube fabric layer formed with such asolution. By increasing the incidence of rafting within nanotube fabriclayers, the density of such fabric layers can be increased, reducingboth the number and size of voids and gaps within such fabric layers.

It should be noted that nanotube elements used and referenced within theembodiments of the present disclosure may be single wall nanotubes,multi-wall nanotubes, or mixtures thereof and may be of varying lengths.Further, the nanotubes may be conductive, semiconductive, orcombinations thereof. Further, the nanotubes may be functionalized (forexample, by oxidation with nitric acid resulting in alcohol, aldehydic,ketonic, or carboxylic moieties attached to the nanotubes), or they maybe non-functionalized.

Nanotube elements may be functionalized for a plurality of reasons. Forexample, certain moieties may be formed on the sidewalls of nanotubeelements to add in the dispersion of those elements within anapplication solution. In another example, certain moieties formed on thesidewalls of nanotube elements can aid in the efficient formation of ananotube fabric. In a further example, nanotube elements can befunctionalized with certain moieties such as to electrically insulatethe sidewalls of the nanotube elements. Nanotube elements can befunctionalized by attaching organic, silica, or metallic moieties (orsome combination thereof) to the sidewalls of the nanotube elements.Such moieties can interact with nanotube elements covalently or remainaffixed through π-π bonding.

While this discussion has been focused on memory, these methods can alsobe used for logic and photovoltaics. Uses for logic are discussedfurther in the present disclosure.

Referring now to FIG. 1A, FIG. 1A illustrates a nonvolatile resistivememory cell 100 in which one or more resistive states storecorresponding logic states in a nonvolatile carbon nanotube (NV CNT)resistive block switch 104 that includes a first conductive terminal 106on an underlying substrate (or insulator), switch nanotube block 108 inelectrical contact with first conductive terminal 106, and a secondconductive terminal 110 in electrical contact with switch nanotube block108. Switch nanotube block 104 is taught by U.S. Patent Pub. No.2008/0160734 and herein incorporated by reference in its entirety.Second conductive terminal 110 is connected to array select line SL andfirst conductive terminal 106 is connected to source S of MOSFET selectdevice 102. Drain D is connected to array bit line BL. Array word lineWL, orthogonal to array bit line BL, forms the gate of MOSFET selectdevice 102. Bit line BL and select line SL are shown as parallel, but SLmay be parallel to WL instead. Nonvolatile resistive memory cell 100includes resistive nonvolatile memory element 104, MOSFET select device102, interconnections, and connections to array lines from cell 100,which is taught by U.S. Pat. No. 7,835,170 and herein incorporated byreference in its entirety.

Nonvolatile resistive memory cell 100 includes one select device (orselect transistor) (1-T) and one nonvolatile resistive memory element(1-R) and may be referred to as a 1-T, 1-R cell type, where the cellselect and nonvolatile storage functions are separate. Also, sinceswitch nanotube block 104 is formed using nanotube fabric layers, arandom access nonvolatile memory formed of multiple nonvolatileresistive memory cells 100 may be referred to as a nanotube randomaccess memory (NRAM®, a registered trademark of Nantero, Inc.). The areaof nonvolatile resistive memory cell 100 may be in the 6F² to 8F² range,where F is the minimum lithographic dimension. Memories formed with cell100 may be fabricated in the low gigabit (10⁹ bit) range but cellscannot be scaled to accommodate order-of-magnitude increases in thetotal number of bits. To achieve such order-of-magnitude increases,nonvolatile memories in the 100 gigabit (10¹¹ bit) and terabit (10¹²bit) range and larger are needed. These require much smaller cell sizesof approximately 4F² and scaling to F values of sub-15 nm. A cell sizeof 4F² requires a single nonvolatile element that combines cell selectand nonvolatile storage functions. Methods and structures that may beused to form such 4F² cells are described further below, including cellswith integrated diode select and nonvolatile resistance functions.

FIG. 1B-1 illustrates a plan view of a two-by-two cross point array 120formed using four interconnected vertically-oriented (3-D) two-terminalnonvolatile carbon nanotube (NV CNT) resistive block switches (130-1,130-2, 130-3, and 130-4). Representative cross section X1-X1′ through aportion of NV CNT block switch 130-1 as illustrated in FIG. 1B-1 furtherillustrates elements of NV CNT block switches in vertically-oriented(3-D) structures as shown in FIG. 1B-2. Representative cross sectionY1-Y1′ through a portion of NV CNT block switch 130-1 as illustrated inFIG. 1B-1 further illustrates elements of NV CNT block switches invertically-oriented (3-D) structures as shown in FIG. 1B-3. Details ofthe two-terminal NV CNT resistive block switches and their methods offabrication, corresponding to NV CNT resistive block switches 130-1,130-2, 130-3, 130-4, and their interconnections, are described furtherabove in U.S. Pat. No. 7,835,170, U.S. Patent Pub. 2008/0160734 and inother incorporated patent references.

Bottom wire (or wiring layer) 122 in FIG. 1B-1 interconnectstwo-terminal NV CNT resistive block switches 130-1 and 130-2 bycontacting bottom (lower level) contacts, with each of thesetwo-terminal NV CNT block switches having dimensions F×F and separatedby a distance F. Bottom wire 124 interconnects two-terminal NV CNTresistive block switches 130-3 and 130-4, forming bottom (lower level)contacts, with each of these two-terminal NV CNT block switches havingdimensions F×F and separated by a distance F. While F represents theminimum feature size to achieve maximum switch array density, dimensionslarger than F may be used as needed. Non-square cross sections may bealso used, e.g. rectangular or circular, to achieve resistance values orother desired features. F may be scaled over a large range ofdimensions: 250 nm and larger, less than 100 nm (e.g. 45 nm or 22 nm),or less than 10 nm. NV CNT resistive block switches with switch nanotubeblock channel lengths L_(SW-CH) in the vertical (Z) direction, definedby the spacing between the first conductor contact and the secondconductor contact, have been fabricated down to less than 30 nm. Incertain applications, L_(SW-CH) may be scaled over a large range: on theorder of 250 nm to on the order of 10 nm. Two-by-two cross point array120 is shown for illustrative purposes; however, cross point arrays of100-by-100, 1,000-by-1,000, 10,000-by-10,000 or larger, may be formed asdescribed further below with respect to FIGS. 2 and 3.

Top wire (or wiring layer) 126 in FIG. 1B-1 interconnects two-terminalNV CNT resistive block switches 130-1 and 130-3 by contacting top (upperlevel) contacts, with each of the two-terminal NV CNT resistive blockswitches having dimensions F×F and separated by a distance F. Top wire128 interconnects two-terminal NV CNT resistive block switches 130-2 and130-4 by contacting top (upper level) contacts, with each of thetwo-terminal NV CNT resistive block switches having dimensions F×F andseparated by a distance F. Top wires 126 and 128 are patterned on thesurface of insulator 132 that fills the regions between the two-terminalNV CNT resistive block switches. While F represents minimum feature sizeto achieve maximum switch array density, dimensions larger than F may beused.

FIG. 1B-2 illustrates cross section X1-X1′ through and along top wire126 in the X direction. The Z direction represents the verticalorientation of two-terminal NV CNT resistive block switch 130-1 and alsoindicates the direction of current flow (vertically) in the ON state.Two-terminal NV CNT resistive block switch 130-1 includes first (lowerlevel) electrical contact 134, which is a section of bottom wire 122;second (upper level) electrical contact 138, which is in contact withtop wire 126; and switch nanotube block 136, which is in electricalcontact with both first electrical contact 134 and second electricalcontact 138. NV CNT resistive block 130-1 may be switched between ON andOFF states multiple times as described in the incorporated patentreferences, e.g., U.S. Pat. No. 7,835,170 and U.S. Patent Pub. No.2008/0160734.

FIG. 1B-3 illustrates cross section Y1-Y1′ through and along bottom wire122 in the Y direction. The Z direction represents the verticalorientation of two-terminal NV CNT resistive block switch 130-1 and alsoindicates the direction (vertically) of current flow in the ON state.Two-terminal NV CNT resistive block switch 130-1 includes firstconductive contact 134, which is a section of bottom wire 122; secondconductive contact 138, which is in contact with top wire 126; andswitch nanotube block 136 in contact with both first conductive contact134 and second conductive contact 138. NV CNT resistive block 130-1 maybe switched between ON and OFF states multiple times as describedfurther above and in the incorporated patent references. The term“conductive” may include metals, metal alloys, semiconductors,silicides, various allotropes of carbon (including amorphous carbon),conductive oxides, and other materials.

FIG. 1C illustrates a nonvolatile resistive change memory cell (orelement) 140 in which one or more resistive states store correspondinglogic states in a nonvolatile carbon nanotube (NV CNT) resistive blockswitch 142 that includes a first conductive terminal 146 in electricalcontact with array wire 144, switch nanotube block 148 in electricalcontact with first conductive terminal 146, and a second conductiveterminal 150 in electrical contact with both switch nanotube block 148and array wire 152. The structure, fabrication, and electrical operationof NV CNT resistive block switch 142, including integration in a CMOSprocess to form memory arrays, is taught by U.S. Patent Pub. No.2008/0160734 and herein incorporated by reference in its entirety.

NV CNT resistive block switch 142 illustrated in FIG. 1C corresponds toNV CNT resistive block switch 104 in FIG. 1A. NV CNT resistive blockswitch 142 also corresponds to NV CNT resistive block switches 130-1,130-2, 130-3, and 130-4 illustrated in FIGS. 1B-1, 1B-2, and 1B-3 incross point array 120. An illustration of NV CNT resistive block switchoperating requirements as a function of array size, such as resistancevalues for R_(ON) and R_(OFF) as a function of cross point array (memoryarray) size, is described further below with respect to FIGS. 2 and 3.

Resistive change memory cell 140 may also be formed with array wire 144in direct contact with the bottom surface of switch nanotube block 148,eliminating the need for first conductive terminal 146. Alternatively,resistive change memory cell 140 may also be formed with array wire 152in direct contact with the top surface of switch nanotube block 148,eliminating the need for second conductive terminal 150. In stillanother implementation, array wire 144 may be in electrical contact withthe bottom surface of switch nanotube block 148 and array wire 152 maybe in electrical contact with the top surface of switch nanotube block148, eliminating the need for first conductive terminal 146 and secondconductive terminal 150, respectively.

The switch nanotube block 148 illustrated in FIG. 1C can be formed bypatterning a nanotube fabric layer or multiple nanotube fabric layers. Ananotube fabric, a nanotube fabric layer, a fabric of nanotubes, ananotube fabric of multiple nanotube fabric layers, a nanofabric, or ananotube block may be used interchangeably in the present disclosure,e.g., a non-woven CNT fabric, may, for example, have a structure ofmultiple entangled nanotubes that are irregularly arranged relative toone another. Alternatively, the fabric of nanotubes for the presentdisclosure may possess some degree of positional regularity of thenanotubes, e.g., some degree of parallelism along their long axes. Suchpositional regularity may be found, for example, on a relatively smallscale wherein flat arrays of nanotubes are arranged together along theirlong axes in rafts on the order of one nanotube long and ten to twentynanotubes wide. In other examples, such positional regularity maybefound on a larger scale, with regions of ordered nanotubes, in somecases, extended over substantially the entire fabric layer. Additionaldescriptions of nanotube fabrics may be found in, for example, U.S. Pat.No. 7,745,810 and U.S. Pat. No. 7,928,523,” both of which areincorporated by reference in their entirety.

Referring now to FIG. 12A, an unordered nanotube fabric layer depositedon a substrate element is shown by scanning electron microscope (SEM)image 1200 illustrated in FIG. 12A. The unordered nanotube fabric layerhas a plurality of nanotubes oriented in a plurality of directions withrespect to each other. The unordered nanotube fabric layer contains gapsand voids between the nanotubes throughout the unordered nanotube fabriclayer.

An ordered nanotube fabric layer formed on a substrate element is shownby SEM image 1250 illustrated in FIG. 12B. The ordered nanotube fabriclayer has a plurality of nanotubes oriented in a substantially paralleldirection with respect to each other and a substantially uniformarrangement along the direction of an applied force. The orderednanotube fabric layer contains adjacent nanotubes grouped together alongtheir sidewalls, reducing or substantially eliminating gaps and voidsbetween nanotubes throughout the ordered nanotube fabric layer. In thenanotube fabric examples illustrated by SEM images 1200 and 1250 inFIGS. 12A and 12B, respectively, both metallic CNTs and semiconductingCNTs are present.

Through the use of an applied force, an unordered nanotube fabric layerdeposited on a substrate element can be rendered into an orderednanotube fabric layer. The applied force includes, but is not limitedto, a directional mechanical force such as a rolling, rubbing, orpolishing force applied to the deposited unordered nanotube fabric layerlinearly, in an arc, or rotationally. In some applications, unorderednanotube fabric layers deposited individually on a substrate elementwill compress into each other under the applied force and thereby reducethe thickness of an ordered nanotube fabric layer. The rendering of anunordered nanotube fabric layer into an ordered nanotube fabric layerthrough the use of an applied force reduces or substantially eliminatesgaps and voids between nanotubes throughout the ordered nanotube fabriclayer and also orients the nanotubes in a substantially paralleldirection with respect to each other. The changes made to a nanotubefabric layer when rendering the nanotube fabric layer from an unorderedlayer into an ordered layer can change the boundary conditions forcurrent flow across the interface or junction between the nanotubefabric layer and conductors or materials electrically contacting thenanotube fabric layer. Additionally, the changes made to a nanotubefabric layer when rendering the nanotube fabric layer from an unorderedlayer into an ordered layer can also change how the current flows thoughthe nanotube fabric layer on a microscopic level by changing frictionalforces that oppose the acceleration of carriers in an electric field.The rendering of an unordered nanotube fabric layer deposited on asubstrate element into an ordered nanotube fabric layer through the useof an applied force is described in more detail in U.S. Patent App. No.61/319,034, incorporated herein by reference in its entirety.

Nanotube fabrics retain the desirable physical properties of thenanotubes from which they are formed. For example, in some electricalapplications, the fabric preferably has a sufficient amount of nanotubesin contact so that at least one electrically conductive orsemi-conductive pathway exists from a given point within the fabric toanother point within the fabric. Nanotubes typically may have a diameterof about 1 to <6 nm depending if they are single-wall or multi-wall andmay have varying lengths. The nanotubes may curve and occasionally crossone another. Gaps in the fabric, i.e., between nanotubes eitherlaterally or vertically, may exist. Such fabrics may comprise singlewall nanotubes, multi-wall nanotubes, or mixtures thereof and may be ofvarying lengths. The nanotubes may be conductive, semiconductive, orcombinations thereof. The fabric may have small areas of discontinuitywith no nanotubes present. The fabric may be prepared as a layer or asmultiple fabric layers, one formed upon another. Fabrics formed asmultiple fabric layers may include a mixture of unordered nanotubefabrics and ordered nanotube fabrics in any combination. The thicknessof the fabric can be chosen as thin as substantially a monolayer ofnanotubes or can be chosen much thicker, e.g., tens of nanometers tohundreds of nanometers in thickness. The porosity of the fabrics canvary from low density fabrics with high porosity to high density fabricswith low porosity. Such fabrics can be prepared by growing nanotubesusing chemical vapor deposition (CVD) processes in conjunction withvarious catalysts, for example. Other methods for generating suchfabrics may involve using spin-coating techniques and spray-coatingtechniques with preformed nanotubes suspended in a suitable solvent,roll-to-roll coating, dip coating, electrostatic spray coating, andprinting processes. Nanoparticles of other materials can be mixed withsuspensions of nanotubes in such solvents and deposited by spin coatingand spray coating to form fabric with nanoparticles dispersed among thenanotubes. The formation of such nanotube layers is taught in several ofthe incorporated references.

For example, U.S. Pat. No. 7,335,395, incorporated herein by referencein its entirety, teaches a plurality of methods for forming nanotubelayers and films on a substrate element using preformed nanotubes. Themethods include, but are not limited to, spin coating (wherein asolution of nanotubes is deposited on a substrate which is then spun toevenly distribute the solution across the surface of the substrate),spray coating (wherein a plurality of nanotubes are suspended within anaerosol solution which is then dispersed over a substrate), roll-to-rollcoating (or roll coating, for brevity) such as Gravure coating (whereinan engraved roller with a surface spinning in a coating bath picks upthe coating solution in the engraved dots or lines of the roller, andwhere the coating is then deposited onto a substrate as it passesbetween the engraved roller and a pressure roller), and dip coating(wherein a plurality of nanotubes are suspended in a solution and asubstrate element is lowered into the solution and then removed).Further, U.S. Pat. No. 7,375,369 to Sen et al. and U.S. Pat. No.7,666,382, both incorporated herein by reference in their entirety,teach solvents that are well suited for suspending nanotubes and forforming nanotube layers and films over a substrate element. For example,such solvents include but are not limited to ethyl lactate, dimethylsulfoxide (DMSO), monomethyl ether, 4-methyl-2 pentanone,N-methylpyrrolidone (NMP), t-butyl alcohol, methoxy propanol, propyleneglycol, ethylene glycol, gamma butyrolactone, benzyl benzoate,salicyladehyde, tetramethyl ammonium hydroxide and esters ofalpha-hydroxy carboxylic acids. Such solvents can disperse the nanotubesto form a stable composition without the addition of surfactants orother surface-active agents.

Referring now to FIG. 1C, first conductive terminal 146 and secondconductive terminal 150 form electrical contacts with the bottom andtop-surface of switch nanotube block 148. The combination of materialsused for these terminals and the switch nanotube block form anddetermine the electrical properties of NV CNT resistive block switch142, such as the minimum values of R_(ON) and the nonlinearity of theresistive change, which determines the R_(ON)-to-R_(OFF) resistanceratio, as described further below with respect to FIG. 3A.

Work function differences between the CNTs in the nanotube fabric andelectrical contacts may be used, for example, to enhance nonlinearity byforming diodes such as Schottky diodes at one contact and near-Ohmiccontact at the other contact as described further below. In addition toselecting various combinations of single wall, multi-wall,semiconducting, and metallic nanotubes when forming the nanotube fabricused in switch nanotube block 148, the nanotubes may also befunctionalized as described further below.

First conductive terminal 146 and second conductive terminal 150 may beformed using a variety of materials. The term “conductive” may includemetals, metal alloys, semiconductors, silicides, conductive oxides,various allotropes of carbon, and other materials. The following areexamples of conductors, conductive alloys, and conductive oxides: Al,Al(Cu), Ag, Au, Bi, Ca, Co, CoSi_(x), Cr, Cu, Fe, In, Ir, Mg, Mo, MoSi₂,Na, Ni, NiSi_(x), Os, Pb, PbSn, PbIn, Pd, Pd₂Si, Pt, PtSi_(x), Rh, RhSi,Ru, RuO, Sb, Sn, Ta, TaN, Ti, TiN, TiAu, TiCu, TiPd, TiSi_(x), TiW, W,WSi₂, Zn, ZrSi₂, and others for example. Some or all of these materialsmay also be used to form arrays wires 144 and 152.

The following are examples of semiconductors that may be used asconductive terminals: Si (doped and undoped), Ge, SiC, GaP, GaAs, GaSb,InP, InAs, InSb, ZnS, ZnSe, CdS, CdSe, CdTe and other examples.

Various allotropes of carbon may also be used as first conductiveterminal 146 and second conductive terminal 150: amorphous carbon (aC);carbon nanotubes such as nanotube fabric terminal, buckyballs, and otherexamples.

Two-terminal NV CNT resistive block switch 142 illustrated in FIG. 1Ccorresponds to two-terminal NV CNT resistive block switches 130-1,130-2, 130-3, and 130-4 illustrated in FIGS. 1B-1, 1B-2, and 1B-3. Arraywire 152 in FIG. 1C, corresponding to top wire 126 in FIGS. 1B-1, 1B-2,and 1B-3, is formed on the surface of insulator 132, and NV CNTresistive block switch 142 is imbedded in dielectric 132 to formtwo-by-two cross point array 120.

1-R memory requirements for relatively high R_(ON) values and relativelyhigh R_(OFF)/R_(ON) ratio values are described further above withrespect to FIG. 1C and further below with respect to FIG. 2B and FIG.3A. Further above, the importance of work function differences betweencontact materials and carbon nanotubes to achieve desirable R_(ON) andR_(OFF) electrical characteristics is described with respect to FIG. 1C.And also, examples of carbon nanotube material options and variousconductive terminal materials are described.

However, in addition to material selection, the geometry and placementof conductive terminals, such as first and second conductive terminals146 and 150, respectively, with respect to switch nanotube blocks, suchas switch nanotube block 148 illustrated in FIG. 1C, may also be used toenhance NV CNT resistive block switch performance. U.S. Patent Pub. No.2008/0160734 gives examples of geometry variations such as the entiretop and bottom surfaces of switch nanotube blocks in contact withconductive terminals as illustrated in FIG. 1C; and, alternatively,conductive terminals only in contact with a portion of top and bottomsurfaces of switch nanotube blocks.

An example of NV CNT resistive block geometry that may be used toincrease R_(ON) and achieve greater resistance nonlinearity is tocontact only a portion of the switch nanotube block on one surface andcompletely contact another surface. For relatively large geometries,50-100 nm or larger for example, a smaller contact area on one surfacerelative to another may be achieved relatively easily as illustrated inU.S. Patent Pub. No. 2008/0160734.

FIG. 1D illustrates a nonvolatile resistive change memory cell 160 inwhich one or more resistive states store corresponding logic states in anonvolatile graphitic resistive block switch 162 that includes a firstconductive terminal 166 in electrical contact with array wire 164,switch graphitic block 168 in electrical contact with first conductiveterminal 166 at contact region 168′, and a second conductive terminal170 in electrical contact with the graphitic block switch 168 at contactregion 168″, and also in electrical contact with array wire 172.

FIG. 1D is similar to FIG. 1C, except that switch nanotube block 148 isreplaced by switch graphitic block 168. The switch graphitic block 168illustrated in FIG. 1D may be formed of a patterned layer or multiplelayers of graphene as described further below with respect to FIG. 5.First conductive terminal 166 corresponds to first conductive terminal146; array wire 164 corresponds to array wire 144; second conductiveterminal 170 corresponds to second conductive terminal 150; and arraywire 172 corresponds to array wire 152. The various conductive terminalsand array wires shown in FIG. 1D may use the same materials as thoselisted with respect to FIG. 1C further above.

NV graphitic resistive block switch 162 illustrated in FIG. 1Dcorresponds to NV CNT resistive block switches 130-1, 130-2, 130-3, and130-4 illustrated in FIGS. 1B-1, 1B-2, and 1B-3 in cross point array120.

Resistive change memory cell 160 may also be formed with array wire 164in direct contact with the bottom surface of switch graphitic block 168,eliminating the need for first conductive terminal 166. Alternatively,resistive change memory cell 160 may also be formed with array wire 172in direct contact with the top surface of the switch graphitic block168, eliminating the need for second conductive terminal 170. In stillanother implementation, array wire 164 may be in electrical contact withthe bottom surface of switch graphitic block 168 and array wire 172 maybe in electrical contact with the top surface of switch graphitic block168, eliminating the need for first conductive terminal 166 and secondconductive terminal 170, respectively.

FIG. 1E illustrates a nonvolatile resistive change memory cell 180 inwhich one or more resistive states store corresponding logic states in anonvolatile buckyball resistive block switch 182 that includes a firstconductive terminal 186 in electrical contact with array wire 184,switch buckyball block 188 in electrical contact with first conductiveterminal 186 at contact region 188′, and a second conductive terminal190 in electrical contact with switch buckyball block 188 at contactregion 188″, and also in electrical contact with array wire 192.

FIG. 1E is similar to FIG. 1C, except that switch nanotube block 148 isreplaced by switch buckyball block 188. Switch buckyball block switch188 illustrated in FIG. 1E may be formed of a patterned layer ormultiple layers of buckyballs as described further below with respect toFIG. 6. First conductive terminal 186 corresponds to first conductiveterminal 146; array wire 184 corresponds to array wire 144; secondconductive terminal 190 corresponds to second conductive terminal 150;and array wire 192 corresponds to array wire 152. The various conductiveterminals and array wires shown in FIG. 1E may use the same materials asthose listed with respect to FIG. 1C further above.

NV buckyball resistive block switch 182 illustrated in FIG. 1Ecorresponds to NV CNT resistive block switches 130-1, 130-2, 130-3, and130-4 illustrated in FIGS. 1B-1, 1B-2, and 1B-3 in cross point array120. An illustration of NV buckyball resistive block switch operatingrequirements as a function of array size, such as resistance values forR_(ON) and R_(OFF) as a function of cross point array (memory array)size, is described further below with respect to FIGS. 2 and 3.

Resistive change memory cell 180 may also be formed with array wire 184in direct contact with the bottom surface of switch buckyball block 188,eliminating the need for first conductive terminal 186. Alternatively,resistive change memory cell 180 may also be formed with array wire 192in direct contact with the top surface of the switch buckyball block188, eliminating the need for second conductive terminal 190. In stillanother implementation, array wire 184 may be in electrical contact withthe bottom surface of the switch buckyball block 188 and array wire 192may be in electrical contact with the top surface of the switchbuckyball block 188, eliminating the need for first conductive terminal186 and second conductive terminal 190, respectively.

Cross point array 200, illustrated schematically in FIG. 2A, representsa 1-R cell-based memory array formed with any kind of cross pointnonvolatile cell, such as a metal oxide cell for example. In the presentdisclosure, cross point array 200 each contains a nonvolatile nanotubeblock switch that corresponds to cross point array 120 illustrated inFIGS. 1B-1, 1B-2, and 1B-3; with nonvolatile 1-R cells 220 and 225corresponding to NV CNT resistive block switches 130-1, 130-2, 130-3,and 130-4; array wires 202, 204, and 206 corresponding to top wires 126and 128; and array wires 212, 214, and 216 corresponding to bottom wires122 and 124. Because 1-R cells 220 and 225 do not include selectdevices, such as MOSFET select device 102 illustrated in FIG. 1A or aselect (steering) diode (not shown) as illustrated in U.S. Patent Pub.No. 2008/0160734. individual two-terminal nonvolatile cross point array1-R cells 220 and 225 need to provide both sufficient selectivity basedon nonlinear resistance values to minimize adjacent cell write or readdisturb, as described further below, and nonvolatile resistance storageof information.

During read and write operations, 1-R cells have parasitic currentflows. A read operation example of the resistive state of 1-R cell 225is illustrated in FIG. 2A in which a read voltage V is applied to arrayline 214 and ground is applied to orthogonal array line 204. A voltageof V/2 is applied to adjacent 1-R cells 220 to minimize the risk ofdisturbing the resistive states of adjacent cells. The read currentincludes current 230 from selected 1-R cell 225 and parasitic currents235 from all the adjacent 1-R cells 220. Parasitic currents limit arraysize in all cross point memories. The size of individual sub-arraysforming the overall memory is dependent on the value of the ON stateresistance R_(ON) and the ratio of the OFF state and ON stateresistances R_(OFF)/R_(ON). This parasitic current problem is well knownand is well documented in the literature. The following reference givesuseful criteria for 1-R memory cell design: Liang, J. et al,“Cross-Point Memory Array Without Cell Selectors—Device Characteristicsand Data Storage Pattern Dependencies”, IEEE Transactions on ElectronDevices, VOL. 57, No. 10, October 2010.

An illustration of cross point array requirements 250 shown in FIG. 2Bdescribes the relationship between the cell minimum ON-state resistanceR_(ON) and the corresponding maximum number of corresponding 1-R cellsas represented by curve 260, a straight line on a log-log plot ascalculated based on assumptions described in the above Liang reference.The nonlinearity resistance requirement, not shown explicitly by curve260, is that the ratio of the OFF-state state resistance R_(OFF) to theON-state resistance R_(ON) (RoFF/RoN) be greater than 2. By way ofexample, a 10⁶ bit array size (point 270 on curve 260) requiresR_(ON)≧3×10⁶ Ohms.

In the process of developing 1-T, 1-R NRAM memories formed using NVresistive memory cell 100 illustrated in FIG. 1A, millions of NV CNTresistive block switches 104 have been fabricated and electricallytested as individual switches on test sites and as part of NRAM memoriesover a wide range of fabrication conditions and using a variety of CNTfabrics (SWNTs, MWNTs, semiconducting, metallic, or combinationsthereof) and conductive terminal materials. ON-state resistance R_(ON)measurements of multiple NV CNT resistive block switches 104 show thatR_(ON) may be controlled over a wide range of resistance values fromless than 1 kΩ to greater than 100 MΩ, which make NV CNT resistive blockswitches a good choice for use in 1-R cross point memory arrays.

In certain applications, during write (SET/RESET) operation, NVresistance memory cell 100 uses MOSFET select device 102 for cellselection and NV CNT resistive block switch 104 for nonvolatileresistance state storage. In operation, R_(ON) values are typicallycontrolled in a range of 100 kΩ to 200 kΩ, for example, to achievenanosecond performance, and R_(OFF) values are typically greater than100 MΩ, with a buffer zone between ON-state and OFF-state resistancevalues of 500 to 1,000 times as described in U.S. patent applicationSer. No. 12/618,448, herein incorporated by reference in its entirety.In this mode of operation, the nonlinearity of NV CNT resistive blockswitch 104 is not typically measured because it does not play a role inmemory cell 100 selection.

However, for resistive memory cells in cross point array (1-R array)configurations, R_(ON) values and nonlinearity as measured by the ratioof R_(OFF)/R_(ON) are important parameters for estimating the maximumnumber of bits in a cross point array, as described further above withrespect to cross point array requirements 250 illustrated in FIG. 2B. Asampling of existing NV CNT resistive block switches 104 were retestedby performing a READ operation using an I-V scan between −2 Volts and +2Volts, with I-V plotted as semi-log plot, for example, I-V curve 300illustrated in FIG. 3A. The switches tested were fabricated usingfabrics with mostly MWNTs and conductive terminals of TiN and W.

Referring to FIG. 3A, in operation, current values are measured at −1 Vand +1 V, representative of typical READ voltage levels in cross pointarrays such as cross point arrays 120 (FIG. 1B) and 200 (FIG. 2A), forexample. From these, R_(ON) and R_(OFF) resistance values and the degreeof nonlinearity of NV CNT resistive block switch 104 (FIG. 1) aredetermined. The current I was approximately 1 μA at +1 V andapproximately 0.2 μA at −1 V, corresponding to a low resistance ON-statevalue of approximately 1 MΩ and a high resistance OFF-state value ofapproximately 5 MΩ, resulting in a high-to-low resistance ratio ofapproximately 5-to-1, well in excess of the required minimum of greaterthan 2-to-1.

FIG. 3B depicts an illustration of cross point array requirements 320,the same curve as cross point array requirements 250 (FIG. 2B), showingthe value of R_(ON)˜1 MΩ at point 330. A horizontal projectionintersects curve 325 at point 335. A vertical projection intersects thehorizontal axis at point 340 corresponding to approximately 4×10⁵ cells,the estimated maximum number of 1-R cells in cross point arrays, such ascross point array 120 (FIG. 1B), for NV CNT resistive blocks switch 104with measured I-V curve 300 (FIG. 3A).

FIG. 3C illustrates resistance values 350 of multiple NV CNT resistiveblock switches, tested as described in U.S. Pat. No. 8,000,127, anddescribed in more detail in U.S. Pat. No. 8,102,018 and hereinincorporated by reference in its entirety. Measured ON-state resistancevalues 352 are in range of ˜800 kΩ to ˜10 MΩ and OFF-state resistancevalues 354 are ˜800 MΩ and greater. NV CNT resistive block switchescorresponding to NV CNT resistive block switch 104 (FIG. 1) and 142(FIG. 1C) were used. NV CNT block switches 104 have been measured (notshown) with ON-state resistance values as high as 100 MΩ. Variousstructures, materials, and geometries described further above withrespect to FIGS. 1C-1E, and further below with respect to FIGS. 4-7, maybe used to enable ON-state resistance values as high as 100 MΩ andR_(OFF)/R_(ON) ratios in excess of two.

FIG. 3D illustrates an SEM of NV CNT resistive block switch 370fabricated using eBeam lithography, which includes switch nanotube block372 that has been scaled to 15 nm by 15 nm dimensions, and electricallycontacted by contacts 374 and 376.

FIG. 3E illustrates resistance values 380 measured on NV CNT resistiveblock switch 370. Resistance values 380 show ON-state resistance valuesduring cycling; that is SET (ON-state), READ, RESET (OFF-state), READ,and so forth. ON-state resistance values 382 and OFF-state resistancevalues 384 are shown across twenty cycles of NV CNT resistive blockswitch 370. ON-state resistance values 382 range from ˜1.5 MΩ to ˜6 MΩ,demonstrating the feasibility of fabricating NV CNT resistive blockswitches scaled to 15 nm dimensions. OFF-state resistance values 384range from ˜200 MΩ to ˜400 MΩ. A description of a 1 Terabit memory chipformed with cross point arrays formed at a 15 nm technology node isdescribed further below with respect to FIG. 21.

At this point in the present disclosure, various carbon based diodes,and enhanced cross point memory cells that include carbon nanotubediodes, are described further below.

Enhanced Cross Point Memory Cells

FIG. 4A illustrates a resistive change memory element 400 having acarbon based diode 410 in a series connection with a nonvolatile carbonnanotube (CNT) resistive block switch 420. The carbon based diode 410illustrated in FIG. 4A is configured as a Schottky diode having aconductive layer 412 electrically contacting a diode nanotube fabriclayer 414. The conductive layer 412 can be formed using any suitablemetal, metal alloy, nitride, oxide, or silicide that has an appropriatework function to form a Schottky contact with the diode nanotube fabriclayer 414. The diode nanotube fabric layer 414 can be formed usingsemiconducting single wall carbon nanotubes (s-SWNTs), as discussed indetail further below, and the diode nanotube fabric layer 414 can bedoped p-type, doped n-type, or intrinsically semiconducting (e.g.undoped), as discussed in detail further below. Therefore, the carbonbased diode 410 configured as a Schottky diode can have an anode formedby the conductive layer 412 and a cathode formed by the diode nanotubefabric layer 414 when the diode nanotube fabric layer 414 is n-type oran anode formed by the diode nanotube fabric layer 414 and a cathodeformed by the conductive layer 412 when the diode nanotube fabric layer414 is p-type. In alternative embodiments, the carbon based diode 410configured as a Schottky diode may be replaced with a pn junction diodeformed using semiconducting single wall carbon nanotubes (s-SWNTs) orany other suitable type of diode that can be formed using s-SWNTs.

The switch nanotube blocks, fabrics, fabric layers illustrated furthercan be a layer (or patterned layer or layers) of multiple,interconnected carbon nanotubes. A nanotube fabric, a nanotube fabriclayer, a fabric of nanotubes, a nanotube fabric of multiple nanotubefabric layers, a nanofabric, or a nanotube block may be usedinterchangeably in the present disclosure, e.g., a non-woven CNT fabric,may for example, have a structure of multiple entangled nanotubes thatare irregularly arranged relative to one another. Alternatively, or inaddition, for example, the fabric of nanotubes for the presentdisclosure may possess some degree of positional regularity of thenanotubes, e.g., some degree of parallelism along their long axes.

The nonvolatile CNT resistive block switch 420 may be formed by a switchnanotube fabric layer 424 located between a first metal layer 422 and asecond metal layer 426. The nonvolatile CNT resistive block switch 420functions similar to the nonvolatile CNT resistive block switch 140(FIG. 1C) discussed above, and therefore will not be described in detailbelow. The first metal layer 422 can be formed using any suitable metal,metal alloy, nitride, oxide, silicide, or carbon that has an appropriatework function to form an ohmic or near ohmic contact with the diodenanotube fabric layer 414. The switch nanotube fabric layer 424 issimilar to the nanotube fabric layer 148 (FIG. 1C) discussed above, andtherefore will not be described in detail below. The second metal layer426 can be formed using metals, metal alloys, nitrides, oxides,silicides, or carbon. The resistive change memory element 400 isillustrated in FIG. 4A with the carbon based diode 410 electricallycontacting a bottom wiring layer 402 and the nonvolatile CNT resistiveblock switch 420 electrically contacting a top wiring layer 404.Alternatively, the resistive change memory element 400 can be configuredto have the carbon based diode 410 electrically contacting the topwiring layer 404 and the nonvolatile CNT resistive block switch 420electrically contacting the bottom wiring layer 402. The bottom wiringlayer 402 and the top wiring layer 404 can be fabricated using suitablemetals, metal alloys, nitrides, oxides, or silicides.

For example, the resistive change memory element 400 is formed by thecarbon based diode 410 and the nonvolatile CNT resistive block switch420 as discussed above. When the diode nanotube fabric layer 414 isformed using p-type semiconducting single wall carbon nanotubes(s-SWNTs) with a work function of about Φ_(P-CNT)≈4.9 eV, the conductivelayer 412 selected should have a work function of less than orapproximately equal to 4.9 eV and the first metal layer 422 should havea work function of greater than or approximately equal to 4.9 eV. In thepresent example, Titanium (Ti) with a work function of about 3.95-4.33eV might be selected for the conductive layer 412 and Platinum (Pt) witha work function of about 5.32-5.5 eV might be selected for the firstmetal layer 422. Although, to reduce costs Titanium Nitride (TiN) with awork function of about 4.83 eV might be selected for the first metallayer 422.

Alternatively, the first metal layer 422 may be eliminated, such as inresistive change memory element 450 illustrated in FIG. 4B with likereference numbers representing like elements and components in FIGS. 4Aand 4B. In the resistive change memory element 450 the interface betweenthe diode nanotube fabric layer 414 and the switch nanotube fabric layer424 forms an ohmic or near ohmic contact. However, when the first metallayer 422 is eliminated the diode nanotube fabric layer 414 might berequired to be a thicker nanotube fabric layer, an ordered nanotubefabric layer, or both to reduce the risk of the diode nanotube fabriclayer 414 being compromised by the application process of putting on theswitch nanotube fabric layer 424. Additionally, the resistive changememory element 450 illustrated in FIG. 4B with the carbon based diode410 electrically contacting the bottom wiring layer 402 and thenonvolatile CNT resistive block switch 420 electrically contacting thetop wiring layer 404 can be configured to have the carbon based diode410 electrically contacting the top wiring layer 404 and the nonvolatileCNT resistive block switch 420 electrically contacting the bottom wiringlayer 402.

The diode nanotube fabric layer 414 can be a thinner nanotube fabriclayer than the switch nanotube fabric layer 424, a nanotube fabric layerof approximately the same thickness as the switch nanotube fabric layer424, or a thicker nanotube fabric layer than the switch nanotube fabriclayer 424. The diode nanotube fabric layer 414 can be a less densenanotube fabric layer than the switch nanotube fabric layer 424, ananotube fabric layer of approximately the same density as the switchnanotube fabric layer 424, or a more dense nanotube fabric layer thanthe switch nanotube fabric layer 424. The diode nanotube fabric layer414 can have a concentration of metallic carbon nanotubes that is lowerthan the concentration of metallic carbon nanotubes in the switchnanotube fabric layer 424. The diode nanotube fabric layer 414 can beformed using semiconducting single wall carbon nanotubes (s-SWNT) withmethods of producing solutions approaching 100% s-SWNTs and removal ofnon-semiconducting SWNTs from nanotube fabrics described further below.Additionally, materials that increase the amount of contact among thes-SWNTs, such as amorphous carbon for example, can be added to the diodenanotube fabric layer 414 to increase the current flow though the diodenanotube fabric layer 414.

The s-SWNTs are typically formed as intrinsic semiconducting elementsthat may be considered p-type semiconducting elements. The s-SWNTs thatare formed as intrinsic semiconducting elements can be converted todoped p-type semiconducting elements or doped n-type semiconductingelements by making the s-SWNTs in an environment with a dopant gaspresent, chemically modifying the s-SWNTs using wet chemistrytechniques, using a chemical vapor deposit process to coat the s-SWNTs,plasma treatment of the s-SWNTs, and ion implantation of the s-SWNTs.Additionally, other carbon allotropes, such as graphitic layers (layeredgraphene) or buckyballs, that are formed as intrinsic semiconductingelements can be converted to doped p-type semiconducting elements ordoped n-type semiconducting elements by making the carbon allotropes inan environment with a dopant gas present, chemically modifying thecarbon allotropes using wet chemistry techniques, using a chemical vapordeposit process to coat the carbon allotropes, plasma treatment of thecarbon allotropes, and ion implantation of the carbon allotropes.

FIG. 4C illustrates an ion implantation device 1400 for in situ dopingof a target material by ion implantation. The target material can be acarbon allotrope such as semiconducting single wall carbon nanotubes,semiconducting graphitic layers, or semiconducting buckyballs. However,the present example uses semiconducting single wall carbon nanotubes asthe target material. The ion implantation device 1400 has an elementalsource (e.g. a dopant gas) 1410, an ion producing coil 1420, anextraction slit 1430, a magnetic region 1440, a magnetic field 1442, amass analyzing slit 1450, a first adjustable voltage difference Ua, asecond adjustable voltage difference Ud, and a current integrator 1460.A nanotube fabric layer 1414 is fabricated on a substrate 1415 and thenanotube fabric layer 1414 can be an ordered nanotube fabric layer orlayers, or an unordered nanotube fabric layer or layer, or combinationsof ordered and unordered nanotube fabric layers. To implant ions intothe nanotube fabric layer 1414 the elemental source (e.g. the dopantgas) 1410 is introduced to the ion producing coil 1420, which energizesthe elemental source (e.g. dopant gas) 1410 and produces ions fromthere. The produced ions are then accelerated by applying the firstadjustable voltage difference Ua; the accelerated ions form a pluralityof ion beams 1425. Only those ion beams 1425 that pass through theextraction slit 1430 may enter into the magnetic region 1440. The ionbeams 1425 are electrically charged, therefore, the ion beams that enterinto the magnetic region 1440 may be deflected by the magnetic field1442 based on, for example, the ions' masses, velocities, and/orcharges. By using the mass analyzing slit 1450, ion beams of high puritymay be extracted from a less pure ion source. After the ionization,extraction, and mass analysis of the elemental source 1410, ion beams1425 may be accelerated or de-accelerated by adjusting the firstadjustable voltage difference Ua and/or the second adjustable voltagedifference Ud. Consequently, the ion implantation device 1400 mayprovide ion beams 1425 of desired energy to impinge the nanotube fabriclayer 1414.

In order to uniformly implant ions into the nanotube fabric layer 1414,the ion beams 1425 may scan across the target materials by for example,an electrostatic technique, a magnetic technique, a mechanicaltechnique, or a combination thereof. Additionally, neutral ions (i.e.ions that are charge neutral) previously included in ion beams 1425 canbe removed from ion beams 1425 by using deflection techniques (e.g.electrostatic and/or magnetic techniques), before ion beams 1425 strikethe nanotube fabric layer 1414. Further, the dosage of implanted ions(i.e. the number of ions implanted per unit area, ions/cm²) in thenanotube fabric layer 1414 may be measured using a Faraday cup detectormounted before the nanotube fabric layer 1414, or an off-set cup mountedbehind the nanotube fabric layer 1414. Given the species, energy, anddosage of the implanted ions, one can specify and adjust theconcentration, depth, and uniformity of ions implanted in the nanotubefabric layer 1414. Examples of chemically active ions (or dopants) thatmay be implanted include atomic species, such as N⁺, F⁺, B⁺, P⁺, As⁺,and Sb⁺, molecular species, such as BF₂ ⁺, B₁₀H₁₄ ⁺, PF₃ ⁺, and AsF₃ ⁺,or any other ion implant species commonly used in the semiconductorindustry to modify the band structure and conductivity of silicon.Further, implanting chemically reactive ion species may require a postthermal anneal following the ion implant to activate the chemicalbonding of the chemically active ion species with carbon (C) andstabilize the structure of the carbon nanotubes.

FIGS. 4D and 4E illustrate an ion implantation process for the nanotubefabric layer 1414, where the nanotube fabric layer 1414 is an unorderednanotube fabric layer and ions 1426 are shown implanted in the nanotubefabric layer 1414. The desired ion dosage in the nanotube fabric layer1414 depends on ion species, ion energy, angle of incidence of ion beams1425, density of the nanotube fabric layer 1414, and thickness of thenanotube fabric layer 1414. FIG. 4D illustrates ion implantation of thenanotube fabric layer 1414 with an angle of incidence of the ion beams1425 being a direct angle (i.e. zero degrees), namely, perpendicular toan upper surface of the nanotube fabric layer 1414. FIG. 4E illustratesion implantation of the nanotube fabric layer 1414 with an angle ofincidence of the ion beams 1425 being greater than zero degrees.Although FIGS. 4D and 4E illustrate ions 1426 being implanted directlyinto the nanotube fabric layer 1414 without any overlying layers, it isto be understood that ions may be implanted indirectly through one ormore overlying layers. The implantation of ions indirectly may berequired to support manufacturing processes where it might be difficultor otherwise inconvenient to implant ions directly into the nanotubefabric layer 1414 prior to the application of one or more overlyinglayers. For example, a first metal layer or other layers may be formedon the nanotube fabric layer 1414 prior to implanting ions. In thepresent example, ions can still be implanted to the desired thicknessrange of the nanotube fabric layer 1414 by properly adjusting theimplant parameters, such as ion species, ion energy, and the angle ofincidence of ion beams. Typically, carbon nanotubes in a nanotube fabriclayer have implant characteristics similar to those of polymers, such asphotoresists used in semiconductor lithography.

The ion implantation embodiments described above are for illustrativeand explanatory purposes only. The ion implantation embodimentsdescribed above are not intended to be exhaustive and are not intendedto limit the scope of the present disclosure to the precise ionimplantation method described above. It is to be understood thatmodification and/or variations are possible in light of the abovedisclosures, or may be acquired from practice of the embodiments.

The primary synthesis technologies for producing CNTs in significantquantities are arc discharge, laser ablation, high pressure carbonmonoxide (HiPCO), Chemical Vapor Deposition (CVD) including PlasmaEnhanced CVD (PECVD), and controlled flame synthesized SWNTs (e.g.,Nano-C). Depending on their physical structure, individual carbonnanotubes can be highly conductive or semiconducting. The conductivityof an individual carbon nanotube is determined by the orientation of thehexagonal rings around the wall of the nanotube. This orientation isreferred to as the chirality (or twist) of the nanotube by those skilledin the art and can be quantified as the angle between the hexagonalpattern of the individual carbon rings making up the wall of thenanotube and the axis of the nanotube itself. In the case ofsemiconducting nanotubes the chirality of the nanotubes is responsiblefor the mobility of holes and/or electrons. Within a typicaldistribution of SWNTs, for example, roughly one third will be conducting(often simply referred to as metallic nanotubes) and two thirds will besemiconducting. Therefore, additional separation techniques are requiredto isolate the s-SWNT from other structures, such as MWNTs and metallicSWNTs.

Current techniques for separating metallic single wall carbon nanotubes(SWNTs) and multi-wall carbon nanotubes (MWNTs) fromsemiconducting-SWNTs result in semiconducting-SWNT concentrations in therange of approximately 80% to just less than 100%, with some metallicCNTs remaining Examples of separation techniques in use aredielectrophoresis (e.g., AC dielectrophoresis and agarose gelelectrophoresis), Gel Chromatography, amine extraction, polymerwrapping, selective oxidation, CNT functionalization, and non-lineardensity-gradient ultracentrifugation. However, additional techniques arebeing developed within the industry to manufacture supplies ofsemiconducting-only carbon nanotubes. Such techniques include methods tosort metallic carbon nanotubes from semiconducting nanotubes, as well asmethods for fabricating carbon nanotubes such that the percentage ofmetallic nanotubes produced is much smaller than the percentage ofsemiconducting nanotubes produced. Presently, >99.5% semiconductingSWNTs have been fabricated. As these techniques continue to develop,supplies of semiconducting-only carbon nanotubes are expected to becomemore readily available and achieve even greater levels of purity. Puritylevels of 99.999% or greater semiconducting SWNTs are being targeted bynanotube suppliers.

Other methods of further processing metallic CNTs, such aspost-processing of metallic CNTs, to either convert them tosemiconducting CNTs or remove them after they have formed thenano-fabric layer may require 1) functionalizing the metallic CNTs sothat they are converted to semiconducting CNTs or non-conducting CNTs(e.g., opens), 2) functionalizing the metallic CNTs so that they can beselectively removed from the nano-fabric layer, or 3) burning-off of themetallic CNTs. Process techniques to convert metallic CNTs tosemiconducting CNTs such as a plasma treatment to convert metallic CNTsto semiconductor type (Chen, et al., Japanese Journal of AppliedPhysics, vol 45, no. 4B, pp. 3680-3685, 2006) or using protein-coatednanoparticles in the device contact areas to convert metallic CNTs tosemiconductor type (Na, et. al., Fullerenes, Nanotubes, and CarbonNanostructures, vol. 14, pp. 141-149, 2006) are further described inthese references. Additionally, the metallic CNTs in the diode nanotubefabric layer 414 that short out the carbon based diode 410 by forming aconductive path can be burnt off because the metallic CNTs have a higherconductivity and lower resistance than the semiconducting CNTs. When anappropriate voltage is applied across the diode nanotube fabric layer414, a burn-off current that flows primarily through metallic CNTs isgenerated causing electrical breakdown or burning off the metallic CNTswhile leaving semiconducting SWNTs intact. The above processingtechniques may be used individually, in combination, or in combinationwith other processing techniques to either remove or convert themetallic CNTs to semiconductor CNTs. The complete conversion or removalof all metallic CNTs from the nanotube fabric layer is not required andmetallic CNTs that are not critical to the diode action may remain inthe nanotube fabric layer.

The diode nanotube fabric layer 414 can be an unordered nanotube fabriclayer with the semiconducting SWNTs in an orientation similar to thatdescribed above and illustrated in FIG. 12A or an ordered nanotubefabric layer with the semiconducting SWNTs in an orientation similar tothat described above and illustrated in FIG. 12B. For a CNT Schottkydiode current flow is created by the flow of majority carriers acrossthe interface or junction between the nanotube fabric layer and theconductive layer. The majority carriers are electrons for a CNT Schottkydiode having an n-type nanotube fabric layer and the majority carriersare holes for a CNT Schottky diode having a p-type nanotube fabriclayer. The changes made to a nanotube fabric layer when rendering thenanotube fabric layer from an unordered layer into an ordered layer canchange the boundary conditions for current flow across the interface orjunction between the nanotube fabric layer and the suitable metal, metalalloy, nitride, oxide, or silicide electrically contacting the nanotubefabric layer. Further, the changes made to a nanotube fabric layer whenrendering the nanotube fabric layer from an unordered layer into anordered layer can also change how the current flows though the nanotubefabric layer on a microscopic level by changing frictional forces thatoppose the acceleration of carriers in an electric field.

The carbon based diodes formed using nanotube fabric layers discussedand shown above in a series connection with the nonvolatile CNTresistive block switch 420 can also be fabricated separately or in aconnection with other devices or components. FIG. 4F illustrates acarbon based diode 470 formed as a Schottky diode having an anode formedby p-type diode nanotube fabric layer 474 and a cathode formed by aconductive layer 472. The p-type diode nanotube fabric layer 474 can bean unordered nanotube fabric layer or an ordered nanotube fabric layerformed using the above stated techniques and methods for forming thediode nanotube fabric layer 474. The conductive layer 472 can be formedusing any suitable metal, metal alloy, nitride, oxide, or silicide thathas an appropriate work function to form a Schottky contact with thep-type diode nanotube fabric layer 474. The p-type diode nanotube fabriclayer 474 is illustrated in FIG. 4F electrically contacting a seconddiode wiring layer 408. The conductive layer 472 is illustrated in FIG.4F electrically contacting a first diode wiring layer 406. The firstdiode wiring layer 406 can be formed using any suitable metal, metalalloy, nitride, oxide, or silicide. The second diode wiring layer 408can be formed using any suitable metal, metal alloy, nitride, oxide, orsilicide that has an appropriate work function to form an ohmic or nearohmic contact with the p-type diode nanotube fabric layer 474.Alternatively, the p-type diode nanotube fabric layer 474 can be inelectrical communication with the first diode wiring layer 406 and theconductive layer 472 can be in electrical communication with the seconddiode wiring layer 408. In this alternative embodiment, the first diodewiring layer 406 can be formed using any suitable metal, metal alloy,nitride, oxide, or silicide that has an appropriate work function toform an ohmic or near ohmic contact with the p-type diode nanotubefabric layer 474 and the second diode wiring layer 408 can be formedusing any suitable metal, metal alloy, nitride, oxide, or silicide.

Further, when the carbon based diode 470 is fabricated as a componentthat can be arranged by a circuit designer, the sequence in which theconducting layer 472 and the p-type diode nanotube fabric layer 474 aredeposited may be based on fabrication parameters; the carbon based diode470 can be rotated by the circuit designer to achieve the desiredpolarity. For example, the conducting layer 472 can be deposited as thebottom layer and the p-type diode nanotube fabric layer 474 can bedeposited as the top layer, so that the p-type diode nanotube fabriclayer 474 can be more easily doped using in situ doping methods andtechniques. Although, the carbon based diode 470 formed as Schottkydiode has been discussed above as being formed using a p-type nanotubefabric layer, the carbon based diode 470 can be formed as a Schottkydiode using an intrinsically semiconducting (e.g. undoped) nanotubefabric layer.

FIG. 4G illustrates a carbon based diode 480 formed as a Schottky diodehaving an anode formed by a conductive layer 482 and a cathode formed byn-type diode nanotube fabric layer 484. The conductive layer 482 can beformed using any suitable metal, metal alloy, nitride, oxide, orsilicide that has an appropriate work function to form a Schottkycontact with the n-type diode nanotube fabric layer 484. The n-typediode nanotube fabric layer 484 can be an unordered nanotube fabriclayer or an ordered nanotube fabric layer formed using the above statedtechniques and methods for forming the diode nanotube fabric layer 474.The n-type diode nanotube fabric layer 484 is illustrated in FIG. 4Gelectrically contacting a first diode wiring layer 406 and theconductive layer 482 is illustrated in FIG. 4G electrically contacting asecond diode wiring layer 408. The first diode wiring layer 406 can beformed using any suitable metal, metal alloy, nitride, oxide, orsilicide that has an appropriate work function to form an ohmic or nearohmic contact with the n-type diode nanotube fabric layer 484. Thesecond diode wiring layer 408 can be formed using any suitable metal,metal alloy, nitride, oxide, or silicide. Alternatively, the n-typediode nanotube fabric layer 484 can be in electrical communication withthe second diode wiring layer 408 and the conductive layer 482 can be inelectrical communication with the first diode wiring layer 406. In thisalternative embodiment, the first diode wiring layer 406 can be formedusing any suitable metal, metal alloy, nitride, oxide, or silicide andthe second diode wiring layer 408 can be formed using any suitablemetal, metal alloy, nitride, oxide, or silicide that has an appropriatework function to form an ohmic or near ohmic contact with the n-typediode nanotube fabric layer 484.

Further, when the carbon based diode 480 is fabricated as a componentthat can be arranged by a circuit designer, the sequence in which theconducting layer 482 and the n-type diode nanotube fabric layer 484 aredeposited may be based on fabrication parameters; the carbon based diode480 can be rotated by the circuit designer to achieve the desiredpolarity. For example, the conducting layer 482 can be deposited as thebottom layer and the n-type diode nanotube fabric layer 484 can bedeposited as the top layer, so that the n-type diode nanotube fabriclayer 484 can be more easily doped using in situ doping methods andtechniques.

FIG. 4H illustrates a carbon based diode 490 formed as a pn junctiondiode having an anode formed by a p-type diode nanotube fabric layer 496and a cathode formed by an n-type diode nanotube fabric layer 498. Thep-type diode nanotube fabric layer 496 can be an unordered nanotubefabric layer or an ordered nanotube fabric layer formed using the abovestated techniques and methods for forming the diode nanotube fabriclayer 474. The n-type diode nanotube fabric layer 498 can be anunordered nanotube fabric layer or an ordered nanotube fabric layerformed using the above stated techniques and methods for forming thediode nanotube fabric layer 484. The use of unordered nanotube fabriclayers, ordered nanotube fabric layers, or an unordered nanotube fabriclayer and an ordered nanotube fabric can change the boundary conditionsfor current flow across the pn junction formed by the p-type diodenanotube fabric layer 496 and the n-type diode nanotube fabric layer498. Additionally, when the p-type diode nanotube fabric layer 496 isformed as an ordered nanotube fabric layer and the n-type diode nanotubefabric layer 498 is formed as an ordered nanotube fabric layer the angleof orientation of the p-type diode nanotube fabric layer 496 relative tothe n-type diode nanotube fabric layer 498 can change the boundaryconditions for current flow across the pn junction. The angle oforientation of the p-type diode nanotube fabric layer 496 relative tothe n-type diode nanotube fabric layer 498 can be selected by a circuitdesigner. For example, the p-type diode nanotube fabric layer 496 can beoriented at an angle of about 90 degrees (i.e. perpendicular) relativeto the n-type diode nanotube fabric layer 498.

The p-type diode nanotube fabric layer 496 is illustrated in FIG. 4Helectrically contacting a first diode wiring layer 406 and the n-typediode nanotube fabric layer 498 is illustrated in FIG. 4H electricallycontacting a second diode wiring layer 408. The first diode wiring layer406 can be formed using any suitable metal, metal alloy, nitride, oxide,or silicide that has an appropriate work function to form an ohmic ornear ohmic contact with the p-type diode nanotube fabric layer 496. Thesecond diode wiring layer 408 can be formed using any suitable metal,metal alloy, nitride, oxide, or silicide that has an appropriate workfunction to form an ohmic or near ohmic contact with the n-type diodenanotube fabric layer 498. Alternatively, the p-type diode nanotubefabric layer 496 can be in electrical communication with the seconddiode wiring layer 408 and the n-type diode nanotube fabric layer 498can be in electrical communication with the first diode wiring layer406. In this alternative embodiment, the first diode wiring layer 406can be formed using any suitable metal, metal alloy, nitride, oxide, orsilicide that has an appropriate work function to form an ohmic or nearohmic contact with the n-type diode nanotube fabric layer 498 and thesecond diode wiring layer 408 can be formed using any suitable metal,metal alloy, nitride, oxide, or silicide that has an appropriate workfunction to form an ohmic or near ohmic contact with the p-type diodenanotube fabric layer 496.

Further, when the carbon based diode 490 is fabricated as a componentthat can be arranged by a circuit designer, the sequence in which thep-type diode nanotube fabric layer 496 and the n-type diode nanotubefabric layer 498 are deposited may be based on fabrication parameters;the carbon based diode 490 can be rotated by the circuit designer toachieve the desired polarity. For example, the n-type diode nanotubefabric layer 498 can be deposited as the bottom layer and the p-typediode nanotube fabric layer 496 can be deposited as the top layer. Inthe present example the n-type diode nanotube fabric layer 498 might berequired to be a thicker nanotube fabric layer, an ordered nanotubefabric layer, or both to reduce the risk of the n-type diode nanotubefabric layer 498 being compromised by the application process of puttingon the p-type nanotube fabric layer 496. The p-type diode nanotubefabric layer 496 might be formed as a thinner nanotube fabric layerand/or the p-type nanotube fabric layer 496 can be more easily dopedusing in situ doping methods and techniques. For example, the p-typediode nanotube fabric layer 496 can be deposited as the bottom layer andthe n-type diode nanotube fabric layer 498 can be deposited as the toplayer. In the present example the p-type diode nanotube fabric layer 496might be required to be a thicker nanotube fabric layer, an orderednanotube fabric layer, or both to reduce the risk of the p-type diodenanotube fabric layer 496 being compromised by the application processof putting on the n-type nanotube fabric layer 498. The n-type diodenanotube fabric layer 498 might be formed as a thinner nanotube fabriclayer and/or the n-type nanotube fabric layer 498 can be more easilydoped using in situ doping methods and techniques. Although, the carbonbased diode 490 formed as a pn junction diode has been discussed aboveas being formed using a p-type nanotube fabric layer and an n-typenanotube fabric layer, the carbon based diode 490 can be formed as a pnjunction diode using an intrinsically semiconducting (e.g. undoped)nanotube fabric layer and an n-type nanotube fabric layer.

FIG. 5A illustrates a resistive change memory element 500 having acarbon based diode 510 in a series connection with a nonvolatile carbonnanotube (CNT) resistive block switch 520. The carbon based diode 510illustrated in FIG. 5A is configured as a Schottky diode having aconductive layer 512 electrically contacting a diode graphitic layer514. The conductive layer 512 can be formed using any suitable metal,metal alloy, nitride, oxide, or silicide that has an appropriate workfunction to form a Schottky contact with the diode graphitic layer 514.The diode graphitic layer 514 can be formed by one or more graphenelayers and the diode graphitic layer 514 can be doped p-type, dopedn-type, or intrinsically semiconducting (e.g. undoped). Therefore, thecarbon based diode 510 configured as a Schottky diode can have an anodeformed by the conductive layer 512 and a cathode formed by the diodegraphitic layer 514 when the diode graphitic layer 514 is n-type or ananode formed by the diode graphitic layer 514 and a cathode formed bythe conductive layer 512 when the diode graphitic layer 514 is p-type.Graphene grows as a 2D zero gap semiconductor and graphene can bepurified and mixed into solution in a similar manner to CNTs, therefore,the diode graphitic layer 514 can be formed using similar methods andtechniques to those discussed above for forming nanotube fabric layers.Additionally, as discussed above for nanotube fabric layers, materialsthat increase the amount of contact among the graphene layers, such asamorphous carbon for example, can be added to the diode graphitic layer514 to increase the current flow through the diode graphitic layer 514.In alternative embodiments, the carbon based diode 510 configured as aSchottky diode may be replaced with a pn junction diode formed using oneor more graphene layers or any other suitable type of diode that can beformed using one or more graphene layers.

The nonvolatile CNT resistive block switch 520 may be formed by a switchnanotube fabric layer 524 located between a first metal layer 522 and asecond metal layer 526. The nonvolatile CNT resistive block switch 520functions similar to the nonvolatile CNT resistive block switch 140(FIG. 1C) discussed above, and therefore, will not be described indetail below. The first metal layer 522 can be formed using any suitablemetal, metal alloy, nitride, oxide, or silicide that has an appropriatework function to form an ohmic or near ohmic contact with the diodegraphitic layer 514. Alternatively, the first metal layer 522 may beeliminated, such as in resistive change memory element 550 illustratedin FIG. 5B with like reference numbers representing like elements andcomponents in FIGS. 5A and 5B. In the resistive change memory element550 the interface between the diode graphitic layer 514 and the switchnanotube fabric layer 524 forms an ohmic or near ohmic contact. Theswitch nanotube fabric layer 524 is similar to the nanotube fabric layer148 (FIG. 1C) discussed above, and therefore, will not be described indetail below. The second metal layer 526 can be formed using metals,metal alloys, nitrides, oxides, or silicides. A bottom wiring layer 502and a top wiring layer 504 can be fabricated using suitable metals,metal alloys, nitrides, oxides, or silicides.

Alternatively, a nonvolatile graphitic resistive block switch 540 may beused in place of the nonvolatile CNT resistive block switch 520, such asin resistive change memory element 560 illustrated in FIG. 5C and inresistive change memory element 570 illustrated in FIG. 5D with likereference numbers representing like elements and components in FIGS.5A-5D. The resistive change memory elements 560 and 570 can be used tostore data by having different resistive states of the resistive changememory elements 560 and 570 correspond to different possible valuesbased on an assigned convention. For example, the resistive changememory elements 560 and 570 can be configured to store a single bit byreversibly switching between a first resistive state (e.g., a highresistive state) that corresponds to a logic 0 and a second resistivestate (e.g., a low resistive state) that corresponds to a logic 1. Inanother example, the resistive change memory elements 560 and 570 can beconfigured to store two bits by reversibly switching between a firstresistive state (e.g., a very high resistive state) that corresponds toa logic 00, a second resistive state (e.g., a moderately high resistivestate) that corresponds to a logic 01, a third resistive state (e.g. amoderately low resistive state) that corresponds to a logic 10, and afourth resistive state (e.g., a very low resistive state) thatcorresponds to a logic 11. Further, the resistive change memory elements560 and 570 can have additional resistive states.

The nonvolatile graphitic resistive block switch 540 can be formed by aswitch graphitic layer 544 in place of the switch nanotube fabric layer524. The switch graphitic layer 544 can be formed using any of theprocessing methods and techniques used to form the diode graphitic layer514, as discussed in detail above. The different resistive states of thenonvolatile graphitic resistive block switch 540 are effectuated throughthe use of the switch graphitic layer 544 that adjusts the resistivestate of the nonvolatile graphitic resistive block switch 540 inresponse to an electrical stimulus. The switch graphitic layer 544 canadjust the nonvolatile graphitic resistive block switch 540 from the lowresistance state that corresponds to logic 1 to the high resistancestate that corresponds to logic 0, through application of a firstelectrical stimulus in the form of a current pulse at an appropriatevoltage to the switch graphitic layer 544. The first electrical stimuluschanges how the current flows on a microscopic level from the firstmetal layer 522. Or, if the first metal layer 522 is not present, fromthe carbon based diode 510 through the switch graphitic layer 544 to thesecond metal layer 526. The switch graphitic layer 544 can adjust thenonvolatile graphitic resistive block switch 540 from the highresistance state that corresponds to logic 0 to the low resistance statethat corresponds to logic 1 through application of a second electricalstimulus in the form of a current pulse at an appropriate voltage to theswitch graphitic layer 544. The second electrical stimulus changes howthe current flows on a microscopic level from the first metal layer 522or if the first metal layer 522 is not present from the carbon baseddiode 510 through the switch graphitic layer 544 to the second metallayer 526.

Further, the resistive change memory elements 500 and 550 illustrated inFIGS. 5A and 5B having the carbon based diode 510 electricallycontacting the bottom wiring layer 502 and the nonvolatile CNT resistiveblock switch 520 electrically contacting the top wiring layer 504 can beconfigured to have the carbon based diode 510 electrically contactingthe top wiring layer 504 and the nonvolatile CNT resistive block switch520 electrically contacting the bottom wiring layer 502. The resistivechange memory elements 560 and 570 illustrated in FIGS. 5C and 5D havingthe carbon based diode 510 electrically contacting the bottom wiringlayer 502 and the nonvolatile graphitic resistive block switch 540contacting the top wiring layer 504 can be configured to have the carbonbased diode 510 electrically contacting the top wiring layer 504 and thenonvolatile graphitic resistive block switch 540 electrically contactingthe bottom wiring layer 502.

The carbon based diodes formed using graphitic layers discussed andshown above in a series connection with the nonvolatile CNT resistiveblock switch 520 and the nonvolatile graphitic resistive block switch540 can also be fabricated separately or in a connection with otherdevices or components. FIG. 5E illustrates a carbon based diode 580formed as a Schottky diode having an anode formed by p-type diodegraphitic layer 584 and a cathode formed a conductive layer 582. Thep-type diode graphitic layer 584 can be formed by one or more graphenelayers and the p-type diode graphitic layer 584 can be formed usingsimilar methods and techniques to those discussed above for forming thediode graphitic layer 514. The conductive layer 582 can be formed usingany suitable metal, metal alloy, nitride, oxide, or silicide that has anappropriate work function to form a Schottky contact with the p-typediode graphitic layer 584. The p-type diode graphitic layer 584 isillustrated in FIG. 5E electrically contacting a second diode wiringlayer 508 and the conductive layer 582 is illustrated in FIG. 5Eelectrically contacting a first diode wiring layer 506. The first diodewiring layer 506 can be formed using any suitable metal, metal alloy,nitride, oxide, or silicide. The second diode wiring layer 508 can beformed using any suitable metal, metal alloy, nitride, oxide, orsilicide that has an appropriate work function to form an ohmic or nearohmic contact with the p-type diode graphitic layer 584. Alternatively,the p-type diode graphitic layer 584 can be in electrical communicationwith the first diode wiring layer 506 and the conductive layer 582 canbe in electrical communication with the second diode wiring layer 508.In this alternative embodiment, the first diode wiring layer 506 can beformed using any suitable metal, metal alloy, nitride, oxide, orsilicide that has an appropriate work function to form an ohmic or nearohmic contact with the p-type diode graphitic layer 584 and the seconddiode wiring layer 508 can be formed using any suitable metal, metalalloy, nitride, oxide, or silicide.

Further, when the carbon based diode 580 is fabricated as a componentthat can be arranged by a circuit designer, the sequence in which theconducting layer 582 and the p-type diode graphitic layer 584 aredeposited may be based on fabrication parameters; the carbon based diode580 can be rotated by the circuit designer to achieve the desiredpolarity. For example, the conducting layer 582 can be deposited as thebottom layer and the p-type diode graphitic layer 584 can be depositedas the top layer, so that the p-type diode graphitic layer 584 can bemore easily doped using in situ doping methods and techniques. Although,the carbon based diode 580 formed as Schottky diode has been discussedabove as being formed using a p-type graphitic layer, the carbon baseddiode 580 can be formed as a Schottky diode using an intrinsicallysemiconducting (e.g. undoped) graphitic layer.

FIG. 5F illustrates a carbon based diode 585 formed as a Schottky diodehaving an anode formed by a conductive layer 586 and a cathode formed byn-type diode graphitic layer 588. The conductive layer 586 can be formedusing any suitable metal, metal alloy, nitride, oxide, or silicide thathas an appropriate work function to form a Schottky contact with then-type diode graphitic layer 588. The n-type diode graphitic layer 588can be formed by one or more graphene layers and the n-type diodegraphitic layer 588 can be formed using similar methods and techniquesto those discussed above for forming the diode graphitic layer 514. Then-type diode graphitic layer 588 is illustrated in FIG. 5F electricallycontacting a first diode wiring layer 506 and the conductive layer 586is illustrated in FIG. 5F electrically contacting a second diode wiringlayer 508. The first diode wiring layer 506 can be formed using anysuitable metal, metal alloy, nitride, oxide, or silicide that has anappropriate work function to form an ohmic or near ohmic contact withthe n-type diode graphitic layer 588. The second diode wiring layer 508can be formed using any suitable metal, metal alloy, nitride, oxide, orsilicide. Alternatively, the n-type diode graphitic layer 588 can be inelectrical communication with the second diode wiring layer 508 and theconductive layer 586 can be in electrical communication with the firstdiode wiring layer 506. In this alternative embodiment, the first diodewiring layer 506 can be formed using any suitable metal, metal alloy,nitride, oxide, or silicide and the second diode wiring layer 508 can beformed using any suitable metal, metal alloy, nitride, oxide, orsilicide that has an appropriate work function to form an ohmic or nearohmic contact with the n-type diode graphitic layer 588.

Further, when the carbon based diode 585 is fabricated as a componentthat can be arranged by a circuit designer, the sequence in which theconducting layer 586 and the n-type diode graphitic layer 588 aredeposited may be based on fabrication parameters; the carbon based diode585 can be rotated by the circuit designer to achieve the desiredpolarity. For example, the conducting layer 586 can be deposited as thebottom layer and the n-type diode graphitic layer 588 can be depositedas the top layer, so that the n-type diode graphitic layer 588 can bemore easily doped using in situ doping methods and techniques.

FIG. 5G illustrates a carbon based diode 590 formed as a pn junctiondiode having an anode formed by a p-type diode graphitic layer 596 and acathode formed by an n-type diode graphitic layer 598. The p-type diodegraphitic layer 596 can be formed by one or more graphene layers and thep-type diode graphitic layer 596 can be formed using similar methods andtechniques to those discussed above for forming the diode graphiticlayer 514. The n-type diode graphitic layer 598 can be formed by one ormore graphene layers and the n-type diode graphitic layer 598 can beformed using similar methods and techniques to those discussed above forforming the diode graphitic layer 514. The p-type diode graphitic layer596 is illustrated in FIG. 5G electrically contacting a first diodewiring layer 506 and the n-type diode graphitic layer 598 is illustratedin FIG. 5G electrically contacting a second diode wiring layer 508. Thefirst diode wiring layer 506 can be formed using any suitable metal,metal alloy, nitride, oxide, or silicide that has an appropriate workfunction to form an ohmic or near ohmic contact with the p-type diodegraphitic layer 596. The second diode wiring layer 508 can be formedusing any suitable metal, metal alloy, nitride, oxide, or silicide thathas an appropriate work function to form an ohmic or near ohmic contactwith the n-type diode graphitic layer 598. Alternatively, the p-typediode graphitic layer 596 can be in electrical communication with thesecond diode wiring layer 508 and the n-type diode graphitic layer 598can be in electrical communication with the first diode wiring layer506. In this alternative embodiment, the first diode wiring layer 506can be formed using any suitable metal, metal alloy, nitride, oxide, orsilicide that has an appropriate work function to form an ohmic or nearohmic contact with the n-type diode graphitic layer 598 and the seconddiode wiring layer 508 can be formed using any suitable metal, metalalloy, nitride, oxide, or silicide that has an appropriate work functionto form an ohmic or near ohmic contact with the p-type diode graphiticlayer 596.

Further, when the carbon based diode 590 is fabricated as a componentthat can be arranged by a circuit designer, the sequence in which thep-type diode graphitic layer 596 and the n-type diode graphitic layer598 are deposited may be based on fabrication parameters; the carbonbased diode 590 can be rotated by the circuit designer to achieve thedesired polarity. For example, the n-type diode graphitic layer 598 canbe deposited as the bottom layer and the p-type diode graphitic layer596 can be deposited as the top layer. In the present example the n-typediode graphitic layer 598 might be required to be a thicker graphiticlayer to reduce the risk of the n-type diode graphitic layer 598 beingcompromised by the application process of putting on the p-typegraphitic layer 596, while the p-type diode graphitic layer 596 might beformed as a thinner graphitic layer and/or the p-type graphitic layer596 can be more easily doped using in situ doping methods andtechniques. For example, the p-type diode graphitic layer 596 can bedeposited as the bottom layer and the n-type diode graphitic layer 598can be deposited as the top layer. In the present example the p-typediode graphitic layer 596 might be required to be a thicker graphiticlayer to reduce the risk of the p-type diode graphitic layer 596 beingcompromised by the application process of putting on the n-typegraphitic layer 598. The n-type diode graphitic layer 598 might beformed as a thinner graphitic layer and/or the n-type graphitic layer598 can be more easily doped using in situ doping methods andtechniques. Although, the carbon based diode 590 formed as a pn junctiondiode has been discussed above as being formed using a p-type graphiticlayer and an n-type graphitic layer, the carbon based diode 590 can beformed as a pn junction diode using an intrinsically semiconducting(e.g. undoped) graphitic layer and an n-type graphitic layer.

FIG. 6A illustrates a resistive change memory element 600 having acarbon based diode 610 in a series connection with a nonvolatile carbonnanotube (CNT) resistive block switch 620. The carbon based diode 610illustrated in FIG. 6A is configured as a Schottky diode having aconductive layer 612 electrically contacting a diode buckyball layer614. The conductive layer 612 can be formed using any suitable metal,metal alloy, nitride, oxide, or silicide that has an appropriate workfunction to form a Schottky contact with the diode buckyball layer 614.The diode buckyball layer 614 can be formed by a layer of semiconductingBuckminsterfullerenes C₆₀, although buckyballs having other shapes andsizes can be used in place of or in combination withBuckminsterfullerenes C₆₀ or buckyballs formed by elements other thancarbon can be used in place of or in combination withBuckminsterfullerenes C₆₀. Additionally, materials that increase theamount of contact among the buckyballs, such as amorphous carbon forexample, can be added to the diode buckyball layer 614 to increase thecurrent flow through the diode buckyball layer 614. The diode buckyballlayer 614 can be doped p-type, doped n-type, or intrinsicallysemiconducting (e.g. undoped). Therefore, the carbon based diode 610configured as a Schottky diode can have an anode formed by theconductive layer 612 and a cathode formed by the diode buckyball layer614 when the diode buckyball layer 614 is n-type or an anode formed bythe diode buckyball layer 614 and a cathode formed by the conductivelayer 612 when the diode buckyball layer 614 is p-type. In alternativeembodiments, the carbon based diode 610 configured as a Schottky diodemay be replaced with a pn junction diode formed using semiconductingbuckyballs or any other suitable type of diode that can be formed usingsemiconducting buckyballs.

The shape of a Buckminsterfullerene C₆₀ is a truncated icosahedrod andresembles a soccer ball. The Buckminsterfullerene C₆₀ is the smallestfullerene molecule where no two pentagons share an edge, therefore,Buckminsterfullerenes C₆₀ are very stable molecules that areintrinsically semiconducting with a small band gap (˜2 eV). TheBuckminsterfullerenes C₆₀ can be purified and mixed into solution;therefore, the diode buckyball layer 614 can be formed using similarmethods and techniques to those discussed above for forming nanotubefabric layers. Because the Buckminsterfullerenes C₆₀ are essentiallyinsoluble in water (˜10⁻¹¹ mg/ml), to mix the Buckminsterfullerenes C₆₀into solution sufficient to form the diode buckyball layer 614 thedispersion of the Buckminsterfullerenes C₆₀ in an aqueous medium has tobe enhanced to achieve a usable level of solubility. Additionally, whenthe Buckminsterfullerenes C₆₀ are dispersed in a solvent there shouldnot be significant coagulation or colloidal formation in the solvent.For example, one method to disperse the Buckminsterfullerenes C₆₀ intoan aqueous solution is to incorporate organic solvents formingadmixtures of water and organic solvents. In the present example, theBuckminsterfullerenes C₆₀ are initially dissolved in an organic solventor organic solvents and then are added to water with strong sonicationfor further dilution. Examples of organic solvents that can dissolveBuckminsterfullerenes C₆₀ include but are not limited to: carbondisulphide, bromoform, toluene, chlorobenzene, and benzene.

The nonvolatile CNT resistive block switch 620 may be formed by a switchnanotube fabric layer 624 located between a first metal layer 622 and asecond metal layer 626. The nonvolatile CNT resistive block switch 620functions similar to the nonvolatile CNT resistive block switch 140(FIG. 1C) discussed above, and therefore, will not be described indetail below. The first metal layer 622 can be formed using any suitablemetal, metal alloy, nitride, oxide, or silicide that has an appropriatework function to form an ohmic or near ohmic contact with the diodebuckyball layer 614. Alternatively, the first metal layer 622 may beeliminated, such as in resistive change memory element 650 illustratedin FIG. 6B with like reference numbers representing like elements andcomponents in FIGS. 6A and 6B. In the resistive change memory element650 the interface between the diode buckyball layer 614 and the switchnanotube fabric layer 624 is in ohmic or near ohmic contact. The switchnanotube fabric layer 624 is similar to the nanotube fabric layer 148(FIG. 1C) discussed above, and therefore, will not be described indetail below. The second metal layer 626 can be formed using metals,metal alloys, nitrides, oxides, or silicides. A bottom wiring layer 602and a top wiring layer 604 can be fabricated using suitable metals,metal alloys, nitrides, oxides, or silicides.

Alternatively, a nonvolatile buckyball resistive block switch 640 may beused in place of the nonvolatile CNT resistive block switch 620, such asin resistive change memory element 660 illustrated in FIG. 6C and inresistive change memory element 670 illustrated in FIG. 6D with likereference numbers representing like elements and components in FIGS.6A-6D. The resistive change memory elements 660 and 670 can be used tostore data by having different resistive states of the resistive changememory elements 660 and 670 correspond to different possible valuesbased on an assigned convention. For example, the resistive changememory elements 660 and 670 can be configured to store a single bit byreversibly switching between a first resistive state (e.g., a highresistive state) that corresponds to a logic 0 and a second resistivestate (e.g., a low resistive state) that corresponds to a logic 1. Inanother example, the resistive change memory elements 660 and 670 can beconfigured to store two bits by reversibly switching between a firstresistive state (e.g., a very high resistive state) that corresponds toa logic 00, a second resistive state (e.g., a moderately high resistivestate) that corresponds to a logic 01, a third resistive state (e.g., amoderately low resistive state) that corresponds to a logic 10, and afourth resistive state (e.g., a very low resistive state) thatcorresponds to a logic 11. Further, the resistive change memory elements660 and 670 can have additional resistive states.

The nonvolatile buckyball resistive block switch 640 can be formed by aswitch buckyball layer 644 in place of the switch nanotube fabric layer624. The switch buckyball layer 644 can be formed using any of theprocessing methods and techniques used to form the diode buckyball layer614, as discussed in detail above. The different resistive states of thenonvolatile buckyball resistive block switch 640 are effectuated throughthe use of the switch buckyball layer 644 that adjusts the resistivestate of the nonvolatile buckyball resistive block switch 640 inresponse to an electrical stimulus. The switch buckyball layer 644 canadjust the nonvolatile buckyball resistive block switch 640 from the lowresistance state that corresponds to logic 1 to the high resistancestate that corresponds to logic 0, through application of a firstelectrical stimulus in the form of a current pulse at an appropriatevoltage to the switch buckyball layer 644. The first electrical stimuluschanges how the current flows on a microscopic level from the firstmetal layer 622 or if the first metal layer 622 is not present from thecarbon based diode 610 through the switch buckyball layer 644 to thesecond metal layer 626. The switch buckyball layer 644 can adjust thenonvolatile buckyball resistive block switch 640 from the highresistance state that corresponds to logic 0 to the low resistance statethat corresponds to logic 1 through application of a second electricalstimulus in the form of a current pulse at an appropriate voltage to theswitch buckyball layer 644. The second electrical stimulus changes howthe current flows on a microscopic level from the first metal layer 622.Or, if the first metal layer 622 is not present, from the carbon baseddiode 610 through the switch buckyball layer 644 to the second metallayer 626.

Further, the resistive change memory elements 600 and 650 illustrated inFIGS. 6A and 6B having the carbon based diode 610 electricallycontacting the bottom wiring layer 602 and the nonvolatile CNT resistiveblock switch 620 electrically contacting the top wiring layer 604 can beconfigured to have the carbon based diode 610 electrically contactingthe top wiring layer 604 and the nonvolatile CNT resistive block switch620 electrically contacting the bottom wiring layer 602. The resistivechange memory elements 660 and 670 illustrated in FIGS. 6C and 6D havingthe carbon based diode 610 electrically contacting the bottom wiringlayer 602 and the nonvolatile buckyball resistive block switch 640contacting the top wiring layer 604 can be configured to have the carbonbased diode 610 electrically contacting the top wiring layer 604 and thenonvolatile buckyball resistive block switch 640 electrically contactingthe bottom wiring layer 602.

The carbon based diodes formed using buckyball layers discussed andshown above in a series connection with the nonvolatile CNT resistiveblock switch 620 and the nonvolatile buckyball resistive block switch640 can also be fabricated separately or in a connection with otherdevices or components. FIG. 6E illustrates a carbon based diode 680formed as a Schottky diode having an anode formed by p-type diodebuckyball layer 684 and a cathode formed a conductive layer 682. Thep-type diode buckyball layer 684 can be formed by a layer ofsemiconducting buckyballs and the p-type diode buckyball layer 684 canbe formed using similar methods and techniques to those discussed abovefor forming the diode buckyball layer 614. The conductive layer 682 canbe formed using any suitable metal, metal alloy, nitride, oxide, orsilicide that has an appropriate work function to form a Schottkycontact with the p-type diode buckyball layer 684. The p-type diodebuckyball layer 684 is illustrated in FIG. 6E electrically contacting asecond diode wiring layer 608 and the conductive layer 682 isillustrated in FIG. 6E electrically contacting a first diode wiringlayer 606. The first diode wiring layer 606 can be formed using anysuitable metal, metal alloy, nitride, oxide, or silicide. The seconddiode wiring layer 608 can be formed using any suitable metal, metalalloy, nitride, oxide, or silicide that has an appropriate work functionto form an ohmic or near ohmic contact with the p-type diode buckyballlayer 684. Alternatively, the p-type diode buckyball layer 684 can be inelectrical communication with the first diode wiring layer 606 and theconductive layer 682 can be in electrical communication with the seconddiode wiring layer 608. In this alternative embodiment, the first diodewiring layer 606 can be formed using any suitable metal, metal alloy,nitride, oxide, or silicide that has an appropriate work function toform an ohmic or near ohmic contact with the p-type diode buckyballlayer 684 and the second diode wiring layer 608 can be formed using anysuitable metal, metal alloy, nitride, oxide, or silicide.

Further, when the carbon based diode 680 is fabricated as a componentthat can be arranged by a circuit designer, the sequence in which theconducting layer 682 and the p-type diode buckyball layer 684 aredeposited may be based on fabrication parameters; the carbon based diode680 can be rotated by the circuit designer to achieve the desiredpolarity. For example, the conducting layer 682 can be deposited as thebottom layer and the p-type diode buckyball layer 684 can be depositedas the top layer, so that the p-type diode buckyball layer 684 can bemore easily doped using in situ doping methods and techniques. Although,the carbon based diode 680 formed as Schottky diode has been discussedabove as being formed using a p-type buckyball layer, the carbon baseddiode 680 can be formed as a Schottky diode using an intrinsicallysemiconducting (e.g. undoped) buckyball layer.

FIG. 6F illustrates a carbon based diode 685 formed as a Schottky diodehaving an anode formed by a conductive layer 686 and a cathode formed byn-type diode buckyball layer 688. The conductive layer 686 can be formedusing any suitable metal, metal alloy, nitride, oxide, or silicide thathas an appropriate work function to form a Schottky contact with then-type diode buckyball layer 688. The n-type diode buckyball layer 688can be formed by a layer of semiconducting buckyballs and the n-typediode buckyball layer 688 can be formed using similar methods andtechniques to those discussed above for forming the diode buckyballlayer 614. The n-type diode buckyball layer 688 is illustrated in FIG.6F electrically contacting a first diode wiring layer 606 and theconductive layer 686 is illustrated in FIG. 6F electrically contacting asecond diode wiring layer 608. The first diode wiring layer 606 can beformed using any suitable metal, metal alloy, nitride, oxide, orsilicide that has an appropriate work function to form an ohmic or nearohmic contact with the n-type diode buckyball layer 688. The seconddiode wiring layer 608 can be formed using any suitable metal, metalalloy, nitride, oxide, or silicide. Alternatively, the n-type diodebuckyball layer 688 can be in electrical communication with the seconddiode wiring layer 608 and the conductive layer 686 can be in electricalcommunication with the first diode wiring layer 606. In this alternativeembodiment, the first diode wiring layer 606 can be formed using anysuitable metal, metal alloy, nitride, oxide, or silicide and the seconddiode wiring layer 608 can be formed using any suitable metal, metalalloy, nitride, oxide, or silicide that has an appropriate work functionto form an ohmic or near ohmic contact with the n-type diode buckyballlayer 688.

Further, when the carbon based diode 685 is fabricated as a componentthat can be arranged by a circuit designer, the sequence in which theconducting layer 686 and the n-type diode buckyball layer 688 aredeposited may be based on fabrication parameters; the carbon based diode685 can be rotated by the circuit designer to achieve the desiredpolarity. For example, the conducting layer 686 can be deposited as thebottom layer and the n-type diode buckyball layer 688 can be depositedas the top layer, so that the n-type diode buckyball layer 688 can bemore easily doped using in situ doping methods and techniques.

FIG. 6G illustrates a carbon based diode 690 formed as a pn junctiondiode having an anode formed by a p-type diode buckyball layer 696 and acathode formed by an n-type diode buckyball layer 698. The p-type diodebuckyball layer 696 can be formed by a layer of semiconductingbuckyballs and the p-type diode buckyball layer 696 can be formed usingsimilar methods and techniques to those discussed above for forming thediode buckyball layer 614. The n-type diode buckyball layer 698 can beformed by a layer of semiconducting buckyballs and the n-type diodebuckyball layer 698 can be formed using similar methods and techniquesto those discussed above for forming the diode buckyball layer 614. Thebuckyballs in the layer of semiconducting buckyballs forming the p-typediode buckyball layer 696 can have shapes and sizes that are differentfrom the shapes and sizes of the buckyballs in the layer ofsemiconducting buckyballs forming the n-type diode buckyball layer 698.For example, the p-type diode buckyball layer 696 can be formed usingtruncated icosahedrod C₆₀ buckyballs and the n-type diode buckyballlayer 698 can be formed using dodecahedral C₂₀ buckyballs. The use oflayers of semiconducting buckyballs where each layer of semiconductingbuckyballs has buckyballs with different shapes and sizes can change theboundary conditions for current flow across the pn junction formed bythe p-type diode buckyball layer 696 and the n-type diode buckyballlayer 698. Additionally, the buckyballs in the layer of semiconductingbuckyballs forming the p-type diode buckyball layer 696 can be formedfrom elements that are different from the elements forming thebuckyballs in the layer of semiconducting buckyballs forming the n-typediode buckyball layer 698. For example, the p-type diode buckyball layer696 can be formed using boron buckyballs and the n-type diode buckyballlayer 698 can be formed using carbon buckyballs. The use of layers ofsemiconducting buckyballs where each layer of semiconducting buckyballshas buckyballs formed from different elements can change the boundaryconditions for current flow across the pn junction formed by the p-typediode buckyball layer 696 and the n-type diode buckyball layer 698.

The p-type diode buckyball layer 696 is illustrated in FIG. 6Gelectrically contacting a first diode wiring layer 606 and the n-typediode buckyball layer 698 is illustrated in FIG. 6G electricallycontacting a second diode wiring layer 608. The first diode wiring layer606 can be formed using any suitable metal, metal alloy, nitride, oxide,or silicide that has an appropriate work function to form an ohmic ornear ohmic contact with the p-type diode buckyball layer 696. The seconddiode wiring layer 608 can be formed using any suitable metal, metalalloy, nitride, oxide, or silicide that has an appropriate work functionto form an ohmic or near ohmic contact with the n-type diode buckyballlayer 698. Alternatively, the p-type diode buckyball layer 696 can be inelectrical communication with the second diode wiring layer 608 and then-type diode buckyball layer 698 can be in electrical communication withthe first diode wiring layer 606. In this alternative embodiment, thefirst diode wiring layer 606 can be formed using any suitable metal,metal alloy, nitride, oxide, or silicide that has an appropriate workfunction to form an ohmic or near ohmic contact with the n-type diodebuckyball layer 698 and the second diode wiring layer 608 can be formedusing any suitable metal, metal alloy, nitride, oxide, or silicide thathas an appropriate work function to form an ohmic or near ohmic contactwith the p-type diode buckyball layer 696.

Further, when the carbon based diode 690 is fabricated as a componentthat can be arranged by a circuit designer, the sequence in which thep-type diode buckyball layer 696 and the n-type diode buckyball layer698 are deposited may be based on fabrication parameters; the carbonbased diode 690 can be rotated by the circuit designer to achieve thedesired polarity. For example, the n-type diode buckyball layer 698 canbe deposited as the bottom layer and the p-type diode buckyball layer696 can be deposited as the top layer. In the present example the n-typediode buckyball layer 698 might be required to be a thickersemiconducting buckyball layer to reduce the risk of the n-type diodebuckyball layer 698 being compromised by the application process ofputting on the p-type buckyball layer 696, while the p-type diodebuckyball layer 696 might be formed as a thinner semiconductingbuckyball layer and/or the p-type buckyball layer 696 can be more easilydoped using in situ doping methods and techniques. For example, thep-type diode buckyball layer 696 can be deposited as the bottom layerand the n-type diode buckyball layer 698 can be deposited as the toplayer. In the present example the p-type diode buckyball layer 696 mightbe required to be a thicker semiconducting buckyball layer to reduce therisk of the p-type diode buckyball layer 696 being compromised by theapplication process of putting on the n-type buckyball layer 698. Then-type diode buckyball layer 698 might be formed as a thinnersemiconducting buckyball layer and/or the n-type buckyball layer 698 canbe more easily doped using in situ doping methods and techniques.Although, the carbon based diode 690 formed as a pn junction diode hasbeen discussed above as being formed using a p-type buckyball layer andan n-type buckyball layer, the carbon based diode 690 can be formed as apn junction diode using; an intrinsically semiconducting (e.g. undoped)buckyball layer and an n-type buckyball layer, a p-type buckyball layerand an intrinsically semiconducting buckyball layer, and twointrinsically semiconducting buckyball layers.

Resistive change memory elements formed by nonvolatile CNT resistiveblock switches in series connections with carbon based diodes formedusing nanotube fabric layers such as the resistive change memory element400 illustrated in FIG. 4A and the resistive change memory element 450illustrated in FIG. 4B can be fabricated in high density cross-pointarrays. For example, FIG. 7A illustrates the resistive change memoryelement 400 fabricated in a high density cross point array, with likereference numbers representing like elements and components in FIGS. 4Aand 7A. Resistive change memory elements formed by nonvolatile CNTresistive block switches in series connections with carbon based diodesformed using graphitic layers such as the resistive change memoryelement 500 illustrated in FIG. 5A and the resistive change memoryelement 550 illustrated in FIG. 5B can be fabricated in high densitycross-point arrays. Resistive change memory elements formed bynonvolatile graphitic resistive block switches in series connectionswith carbon based diodes formed using graphitic layers such as theresistive change memory element 560 illustrated in FIG. 5C and theresistive change memory element 570 illustrated in FIG. 5D can befabricated in high density cross-point arrays. For example, FIG. 7Billustrates the resistive change memory element 500 fabricated in a highdensity cross-point array, with like reference numbers representing likeelements and components in FIGS. 5A and 7B. Resistive change memoryelements formed by nonvolatile CNT resistive block switches in seriesconnections with a carbon based diodes formed using buckyballs layersuch as the resistive change memory element 600 illustrated in FIG. 6Aand the resistive change memory element 650 illustrated in FIG. 6B canbe fabricated in high density cross-point arrays. Resistive changememory elements formed by nonvolatile buckyball resistive block switchesin series connections with carbon based diodes formed using buckyballlayers such as the resistive change memory element 660 illustrated inFIG. 6C and the resistive change memory element 670 illustrated in FIG.6D can be fabricated in high density cross-point arrays. For example,FIG. 7C illustrates the resistive change memory element 600 fabricatedin a high density cross-point array, with like reference numbersrepresenting like elements and components in FIGS. 6A and 7C.

FIG. 8A illustrates an example of a process flow 1850 for fabricatingresistive change memory elements in a high density cross-point array.The process flow 1850 is discussed in detail below and the process flow1850 is directed toward fabricating resistive change memory elementshaving nonvolatile CNT resistive block switches in series connectionswith carbon based diodes formed using nanotube fabric layers, such asresistive change memory elements 400 and 450 illustrated in FIGS. 4A and4B. The fabrication processes for other resistive change memory elementsdescribed in other embodiments, such as resistive change memory elements500, 550, 560, and 570 illustrated in FIGS. 5A-5D and resistive changememory elements 600, 650, 660, and 670 illustrated in FIGS. 6A-6D, aresimilar to the process flow 1850. Therefore, the process flow 1850 isgenerally applicable to the resistive change memory elements describedin other embodiments. The process flow 1850 is an example of a processfor fabricating resistive change memory elements in a high densitycross-point array and other processes for fabricating resistive changememory elements in a high density cross-point array, such as damascenebased processes, can be used. The process flow 1850 is not required tobe a standalone fabrication process and the process flow 1850 can be apart of other fabrication processes or the process flow 1850 can be usedin combination with other fabrication processes. The steps described andshown in the process flow 1850 can be performed in orders other than theorder described and shown. Further, select steps from the process flow1850 can be a part of other fabrication processes or select steps fromthe process flow 1850 can be used in combination with other fabricationprocesses.

The process flow 1850 for fabricating resistive change memory elementsin a high density cross-point array begins after chemical mechanicalplanarization (CMP) of a starting wafer. FIG. 8B illustrates a startingwafer 801 having a smooth surface after chemical mechanicalplanarization of an insulating layer 803, a first conductive layer 812,and a second conductive layer 832. The insulating layer 803 has viaholes for the first conductive layer 812 and the second conductive layer832 and the insulating layer 803 is formed on a bottom wiring layer 802.The first conductive layer 812 is formed using any suitable metal, metalalloy, nitride, oxide, or silicide that has an appropriate work functionto form a Schottky contact with a later deposited diode nanotube fabriclayer. The first conductive layer 812 is formed electrically contactingthe bottom wiring layer 802. The second conductive layer 832 is formedusing any suitable metal, metal alloy, nitride, oxide, or silicide thathas an appropriate work function to form a Schottky contact with a laterdeposited diode nanotube fabric layer. The second conductive layer 832is formed electrically contacting the bottom wiring layer 802. Thestarting wafer 801 can have a substrate element, additional layers,logic devices, and/or circuitry located below the bottom wiring layer802, however the substrate element, additional layers, logic devices,and/or circuitry have been omitted from FIG. 8B for simplicity ofillustration. For example, logic devices and circuitry that form amemory device can be located below the bottom wiring layer 802 and thelogic devices and circuitry can be electrically connected with theresistive change memory elements through bottom wiring layer 802.

The process flow 1850 begins with depositing layers of materials thatform Schottky diodes and nonvolatile CNT resistive block switches on thesmooth surface of the starting wafer 801. FIG. 8C illustrates a diodenanotube fabric layer 813, a bottom metal layer 821, a switch nanotubefabric layer 823, and a top metal layer 825 deposited on the smoothsurface of the starting wafer 801. The diode nanotube fabric layer 813can be deposited by spin coating, spray coating, roll-to-roll coating,dip coating, electrostatic spray coating, or printing processes, asdiscussed in detail above. The diode nanotube fabric layer 813 is inelectrical contact with the first conductive layer 812 and the secondconductive layer 832. The diode nanotube fabric layer 813 can bedeposited as an unordered nanotube fabric layer or as an orderednanotube fabric layer. When the diode nanotube fabric layer 813 isdeposited as an unordered nanotube fabric layer and an ordered nanotubefabric layer is desired, a step for rendering an unordered nanotubefabric layer into an ordered nanotube fabric layer can be included. Thesemiconducting single wall carbon nanotubes (s-SWNTs) that form thediode nanotube fabric layer 813 can be deposited as intrinsicallysemiconducting elements, doped p-type semiconducting elements, or dopedn-type semiconducting elements. The s-SWNTs can be doped before beingdeposited or doped after being deposited using the doping methods andtechniques discussed in detail above. When the s-SWNTs are deposited asintrinsically semiconducting elements and doped p-type semiconductingelements or doped n-type semiconducting elements are desired, a step fordoping the s-SWNTs can be included. The deposited s-SWNTs can be dopeddirectly before the bottom metal layer 821 is deposited or the s-SWNTscan be doped indirectly after any of the bottom metal layer 821, theswitch nanotube fabric layer 823, and the top metal layer 825 isdeposited. Additionally, any of the processing methods and techniquesused to form the diode nanotube fabric layer 414, as discussed above,can be included.

The bottom metal layer 821 can be deposited by physical vapor deposition(PVD) or chemical vapor deposition (CVD). The bottom metal layer 821forms an ohmic or near ohmic contact with the diode nanotube fabriclayer 813 and the bottom metal layer 821 forms the bottom electrode ofthe nonvolatile CNT resistive block switch. The switch nanotube fabriclayer 823 can be deposited by spin coating, spray coating, roll-to-rollcoating, dip coating, electrostatic spray coating, or printingprocesses, as discussed in detail above. The switch nanotube fabriclayer 823 can be deposited as an unordered nanotube fabric layer or asan ordered nanotube fabric layer. When the switch nanotube fabric layer823 is deposited as an unordered nanotube fabric layer and an orderednanotube fabric layer is desired, a step for rendering an unorderednanotube fabric layer into an ordered nanotube fabric layer, asdiscussed in detail above, can be included. When an adjustment to arange of resistivity and/or resistive states of the switch nanotubefabric layer 823 is desired, a step for adjusting the range ofresistivity and/or the resistive states of the switch nanotube fabriclayer 823, as discussed in detail in U.S. patent application Ser. No.12/874,501, can be included. Additionally, any of the processing methodsand techniques used to form the switch nanotube fabric layer 424, asdiscussed above, can be included. The switch nanotube fabric layer 823can have a concentration of metallic carbon nanotubes that is higherthan the concentration of metallic carbon nanotube in the diode nanotubefabric layer 813. The top metal layer 825 can deposited by physicalvapor deposition (PVD) or chemical vapor deposition (CVD); the top metallayer 825 forms the top electrode/contact of the nonvolatile CNTresistive block switch.

The deposition of the diode nanotube fabric layer 813, the bottom metallayer 821, the switch nanotube fabric layer 823, and the top metal layer825 creates a stack that is subsequently patterned and etched to thesmooth surface of the starting wafer 801. The patterning and etching ofthe stack forms a first diode nanotube fabric layer 814, a second diodenanotube fabric layer 834, a first bottom metal layer 822, a secondbottom metal layer 842, a first switch nanotube fabric layer 824, asecond nanotube fabric layer 844, a first top metal layer 826, and asecond top metal layer 846 as illustrated in FIG. 8D. Following thepattern and etch of the stack and a post etch clean, a sidewallpassivation and a dielectric fill between the stacks in the array aredone by depositing a dielectric fill for sidewall passivation 850, suchas but not limited to SiN, and a dielectric fill between the stacks 852,such as but not limited to SiO₂, as illustrated in FIG. 8E. However,those skilled in the art will note many options, depending on arraypitch and topology, are available.

After the dielectric depositions, the array topology is planarized tothe first top metal layer 826 and the second top metal layer 846 using aplanarization process, such as but not limited chemical mechanicalplanarization (CMP), so that the first top metal layer 826 and thesecond top metal layer 846 are exposed. Following planarization andcleaning of the first top metal layer 826, the second top metal layer846, the dielectric fill for sidewall passivation 850, and thedielectric fill between the stacks 852, a top wiring layer fabricationis performed by depositing a metal film such as Al, Cu, or othersuitable metal, metal alloy, nitride, oxide, or silicide. The top wiringlayer is then patterned and plasma metal etched to form a first topwiring layer 804 and a second top wiring layer 805 as illustrated by asingle-level nonvolatile resistive change memory 800 in FIG. 8F.

The single-level nonvolatile resistive change memory 800 shown in FIG.8F has a first resistive change memory element 860 and a secondresistive change memory element 870. The first resistive change memoryelement 860 is formed by a first nonvolatile CNT resistive block switchin a series connection with a first carbon based diode configured as aSchottky diode. The first nonvolatile CNT resistive block switch isformed by the first bottom metal layer 822, the first switch nanotubefabric layer 824, and the first top metal layer 826. The first carbonbased diode is formed by the first conductive layer 812 and the firstdiode nanotube fabric layer 814. The second resistive change memoryelement 870 is formed by a second nonvolatile CNT resistive block switchin a series connection with a second carbon based diode configured as aSchottky diode. The second nonvolatile CNT resistive block switch isformed by the second bottom metal layer 842, the second switch nanotubefabric layer 844, and the second top metal layer 846. The second carbonbased diode is formed by the second conductive layer 832 and the seconddiode nanotube fabric layer 834. Although not shown in FIG. 8F, thefirst resistive change memory element 860 and the second resistivechange memory element 870 can have carbon based diodes configured as pnjunction diodes formed in place of the carbon based diodes configured asSchottky diodes. The carbon based diodes configured as pn junctiondiodes can be formed by depositing nanotube fabric layers in place ofthe first conductive layer 812 and the second conductive layer 832 onthe starting wafer 801.

The formation of ohmic or near ohmic contacts between materials, such asmetals, metal alloys, nitrides, oxides, silicides, and semiconductorsfrequently includes a high temperature annealing step that reducesunintentional barriers at the interfaces of the materials. In theexample shown in FIGS. 8A-8F, a high temperature annealing step can beincluded that reduces unintentional barriers at the interfaces betweenthe first and second bottom metal layers and the first and second diodenanotube fabric layers and at the interfaces between the first andsecond top metal layers and the first and second switch nanotube fabriclayers. Typically, but not limited to, the high temperature annealingstep is done at approximately 475° C. in a reducing ambient such asforming gas (20:1 N₂/H₂). Although, the high temperature annealing stepcan improve the formation of ohmic or near ohmic contacts between thefirst and second bottom metal layers and the first and second diodenanotube fabric layers and between the first and second top metal layersand the first and second switch nanotube fabric layers, the hightemperature annealing step should be optimized to not significantlyadversely affect the Schottky diode action between the first and secondconductive layers and the first and second diode nanotube fabric layers.

Additional steps for fabricating a multi-level nonvolatile resistivechange memory can be included to the process flow for fabricatingresistive change memory elements in a high density cross-point array asshown in FIGS. 8A-8F and discussed in detail above. The additional stepsfor fabricating the multi-level nonvolatile resistive change memory canbe added after fabrication of a single-level nonvolatile resistivechange memory. FIG. 9A illustrates a single-level nonvolatile resistivechange memory 900 that can be fabricated in a similar manner to thesingle-level nonvolatile resistive change memory 800 shown in FIG. 8Fand discussed in detail above. The single-level nonvolatile resistivechange memory 900 is formed by a bottom wiring layer 902, an insulatinglayer 903, a first conductive layer 912, a second conductive layer 932,a first diode nanotube fabric layer 914, a second diode nanotube fabriclayer 934, a first bottom metal layer 922, a second bottom metal layer942, a first switch nanotube fabric layer 924, a second switch nanotubefabric layer 944, a first top metal layer 926, a second top metal layer946, a dielectric fill for sidewall passivation 950, a dielectric fillbetween the stacks 952, a first common wiring layer 904, and a secondcommon wiring layer 905.

The single-level nonvolatile resistive change memory 900 illustrated inFIG. 9A has a first resistive change memory element 960 and a secondresistive change memory element 970. The first resistive change memoryelement 960 is formed by a first nonvolatile CNT resistive block switchin a series connection with a first carbon based diode configured as aSchottky diode. The first nonvolatile CNT resistive block switch isformed by the first bottom metal layer 922, the first switch nanotubefabric layer 924, and the first top metal layer 926. The first carbonbased diode is formed by the first conductive layer 912 and the firstdiode nanotube fabric layer 914. The second resistive change memoryelement 970 is formed by a second nonvolatile CNT resistive block switchin a series connection with a second carbon based diode configured as aSchottky diode. The second nonvolatile CNT resistive block switch isformed by the second bottom metal layer 942, the second switch nanotubefabric layer 944, and the second top metal layer 946. The second carbonbased diode is formed by the second conductive layer 932 and the seconddiode nanotube fabric layer 934. Although not shown in FIG. 9A, thefirst resistive change memory element 960 and the second resistivechange memory element 970 can have carbon based diodes configured as pnjunction diodes formed in place of the carbon based diodes configured asSchottky diodes. The carbon based diodes configured as pn junctiondiodes can be formed by depositing nanotube fabric layers in place ofthe first conductive layer 912 and the second conductive layer 932.

The additional steps for fabricating a multi-level nonvolatile resistivechange memory begin with depositing a sufficiently thick dielectriclayer 954 on top of the first common wiring layer 904 and the secondcommon wiring layer 905 of the single-level nonvolatile resistive changememory 900. The thick dielectric layer 954 is then planarized andcontact vias are patterned and etched through the thick dielectric layer954 stopping on the first common wiring layer 904 and the second commonwiring layer 905. After the contact etch and a resist removal/clean, athird top metal layer 925 is deposited on top of the first common wiringlayer 904 and a fourth top metal layer 945 is deposited on top of thesecond common wiring layer 905. A chemical mechanical planarization(CMP) of the thick dielectric layer 954, the third top metal layer 925,and the fourth top metal layer 945 is performed following the depositionas illustrated in FIG. 9A. A third switch nanotube fabric layer 923, afourth switch nanotube fabric layer 943, a third bottom metal layer 921,a fourth bottom metal layer 941, a third diode nanotube fabric layer913, a fourth diode nanotube fabric layer 933, a third conductive layer911, a fourth conductive layer 931, a dielectric fill for sidewallpassivation 951, a dielectric fill between the stacks 953, and a topwiring layer 906 are then formed above the third top metal layer 925 andthe fourth top metal layer 945 as illustrated in FIG. 9B. The thirdswitch nanotube fabric layer 923, the fourth switch nanotube fabriclayer 943, the third bottom metal layer 921, the fourth bottom metallayer 941, the third diode nanotube fabric layer 913, the fourth diodenanotube fabric layer 933, the third conductive layer 911, the fourthconductive layer 931, and the top wiring layer 906 are formed in asimilar manner but with the order being reversed from the first switchnanotube fabric layer 824, the second switch nanotube fabric layer 844,the first bottom metal layer 822, the second bottom metal layer 842, thefirst diode nanotube fabric layer 814, the second diode nanotube fabriclayer 834, the first conductive layer 812, the second conductive layer832, and the top wiring layer discussed in detail above with respect tothe single-level nonvolatile resistive change memory 800.

FIG. 9B illustrates a multi-level nonvolatile resistive change memory901 having a third resistive change memory element 980 and a fourthresistive change memory element 990 vertically stacked above the firstresistive change memory element 960 and the second resistive changememory element 970 of the single-level nonvolatile resistive changememory 900. The third resistive change memory element 980 is formed by athird nonvolatile CNT resistive block switch in a series connection witha third carbon based diode configured as a Schottky diode. The thirdnonvolatile CNT resistive block switch is formed by the third bottommetal layer 921, the third switch nanotube fabric layer 923, and thethird top metal layer 925. The third carbon based diode is formed by thethird conductive layer 911 and the third diode nanotube fabric layer913. The fourth resistive change memory element 990 is formed by afourth nonvolatile CNT resistive block switch in a series connectionwith a fourth carbon based diode configured as Schottky diode. Thefourth nonvolatile CNT resistive block switch is formed by the fourthbottom metal layer 941, the fourth switch nanotube fabric layer 943, andthe fourth top metal layer 945. The fourth carbon based diode is formedby the fourth conductive layer 931 and the fourth diode nanotube fabriclayer 933. The first common wiring layer 904 can operate as a commonwordline for the first resistive change memory element 960 and the thirdresistive change memory element 980. The second common wiring layer 905can operate as a common wordline for the second resistive change memoryelement 970 and the fourth resistive change memory element 990. Althoughnot shown in FIG. 9B, the first resistive change memory element 960, thesecond resistive change memory element 970, the third resistive changememory element 980, and the fourth resistive change memory element 990can have carbon based diodes configured as pn junction diodes formed inplace of the carbon based diodes configured as Schottky diodes. Thecarbon based diodes configured as pn junction diodes can be formed bydepositing nanotube fabric layers in place of the first conductive layer912, the second conductive layer 932, the third conductive layer 911,and the fourth conductive layer 931.

Further, the multi-level nonvolatile resistive change memory 901 canhave additional resistive change memory elements vertically stackedabove the third resistive change memory element 980 and the fourthresistive change memory element 990. The additional resistive changememory elements can be formed by repeating the additional steps forfabricating a multi-level nonvolatile resistive change memory withproper logic to address the multi-level memory array being incorporatedinto the memory device. The number of vertically stacked resistivechange memory elements is a design variable that can be selected by acircuit designer with the additional steps for fabricating a multi-levelnonvolatile resistive change memory element being repeated.

FIG. 10A illustrates a single-level nonvolatile resistive change memory1000 that can be fabricated in a similar manner to the single-levelnonvolatile resistive change memory 800 shown in FIG. 8F and discussedin detail above. However, the fabrication process for the single-levelnonvolatile resistive change memory 1000 should deposit a diodegraphitic layer in place of the diode nanotube fabric layer depositedfor the single-level nonvolatile resistive change memory 800. The diodegraphitic layer can be formed using any of the processing methods andtechniques used to form the diode graphitic layer 514, as discussed indetail above. The single-level nonvolatile resistive change memory 1000is formed by a bottom wiring layer 1002, an insulating layer 1003, afirst conductive layer 1012, a second conductive layer 1032, a firstdiode graphitic layer 1014, a second diode graphitic layer 1034, a firstbottom metal layer 1022, a second bottom metal layer 1042, a firstswitch nanotube fabric layer 1024, a second switch nanotube fabric layer1044, a first top metal layer 1026, a second top metal layer 1046, adielectric fill for sidewall passivation 1050, a dielectric fill betweenthe stacks 1052, a first common wiring layer 1004, and a second commonwiring layer 1005.

The single-level nonvolatile resistive change memory 1000 illustrated inFIG. 10A has a first resistive change memory element 1060 and a secondresistive change memory element 1070. The first resistive change memoryelement 1060 is formed by a first nonvolatile CNT resistive block switchin a series connection with a first carbon based diode configured as aSchottky diode. The first nonvolatile CNT resistive block switch isformed by the first bottom metal layer 1022, the first switch nanotubefabric layer 1024, and the first top metal layer 1026. The first carbonbased diode is formed by the first conductive layer 1012 and the firstdiode graphitic layer 1014. The second resistive change memory element1070 is formed by a second nonvolatile CNT resistive block switch in aseries connection with a second carbon based diode configured as aSchottky diode. The second nonvolatile CNT resistive block switch isformed by the second bottom metal layer 1042, the second switch nanotubefabric layer 1044, and the second top metal layer 1046. The secondcarbon based diode is formed by the second conductive layer 1032 and thesecond diode graphitic layer 1034.

Although not shown in FIG. 10A, the first resistive change memoryelement 1060 and the second resistive change memory element 1070 canhave nonvolatile graphitic resistive block switches formed in place ofthe nonvolatile CNT resistive block switches. The nonvolatile graphiticresistive block switches can be formed by depositing a switch graphiticlayer in place of the switch nanotube fabric layer. The switch graphiticlayer can be formed using any of the processing methods and techniquesused to form the switch graphitic layer 544, as discussed in detailabove. Further, the first resistive change memory element 1060 and thesecond resistive change memory element 1070 can have carbon based diodesconfigured as pn junction diodes formed in place of the carbon baseddiodes configured as Schottky diodes. The carbon based diodes configuredas pn junction diodes can be formed by depositing graphitic layers inplace of the first conductive layer 1012 and the second conductive layer1032.

FIG. 10B illustrates a multi-level nonvolatile resistive change memory1001 having a third resistive change memory element 1080 and a fourthresistive change memory element 1090 vertically stacked above the firstresistive change memory element 1060 and the second resistive changememory element 1070 of the single-level nonvolatile resistive changememory 1000. The multi-level nonvolatile resistive change memory 1001 isformed by the bottom wiring layer 1002, the insulating layer 1003, thefirst conductive layer 1012, the second conductive layer 1032, the firstdiode graphitic layer 1014, the second diode graphitic layer 1034, thefirst bottom metal layer 1022, the second bottom metal layer 1042, thefirst switch nanotube fabric layer 1024, the second switch nanotubefabric layer 1044, the first top metal layer 1026, the second top metallayer 1046, the dielectric fill for sidewall passivation 1050, thedielectric fill between the stacks 1052, the first common wiring layer1004, and the second common wiring layer 1005, as discussed in detailabove with respect to the single-level nonvolatile resistive changememory 1000 with like reference numbers representing like elements andcomponents in FIGS. 10A and 10B. The multi-level nonvolatile resistivechange memory 1001 is additionally formed by a thick dielectric layer1054, a third top metal layer 1025, a fourth top metal layer 1045, athird switch nanotube fabric layer 1023, a fourth switch nanotube fabriclayer 1043, a third bottom metal layer 1021, a fourth bottom metal layer1041, a third diode graphitic layer 1013, a fourth diode graphitic layer1033, a third conductive layer 1011, a fourth conductive layer 1031, adielectric fill for sidewall passivation 1051, a dielectric fill betweenthe stacks 1053, and a top wiring layer 1006.

The first resistive change memory element 1060 and the second resistivechange memory element 1070 can be fabricated as discussed in detailabove with respect to the single-level nonvolatile resistive changememory 1000 with like reference numbers representing like elements andcomponents in FIGS. 10A and 10B. The third resistive change memoryelement 1080 and the fourth resistive change memory element 1090 can befabricated in a similar manner to the third resistive change memoryelement 980 and the fourth resistive change memory element 990illustrated in FIG. 9B. However, the fabrication process for the thirdresistive change memory element 1080 and the fourth resistive changememory element 1090 should deposit a diode graphitic layer in place ofthe diode nanotube fabric layer deposited for the third resistive changememory element 980 and the fourth resistive change memory element 990illustrated in FIG. 9B. The diode graphitic layer can be formed usingany of the processing methods and techniques used to form the diodegraphitic layer 514, as discussed in detail above.

The first resistive change memory element 1060 is formed by a firstnonvolatile CNT resistive block switch in a series connection with afirst carbon based diode configured as a Schottky diode. The firstnonvolatile CNT resistive block switch is formed by the first bottommetal layer 1022, the first switch nanotube fabric layer 1024, and thefirst top metal layer 1026. The first carbon based diode is formed bythe first conductive layer 1012 and the first diode graphitic layer1014. The second resistive change memory element 1070 is formed by asecond nonvolatile CNT resistive block switch in a series connectionwith a second carbon based diode configured as a Schottky diode. Thesecond nonvolatile CNT resistive block switch is formed by the secondbottom metal layer 1042, the second switch nanotube fabric layer 1044,and the second top metal layer 1046. The second carbon based diode isformed by the second conductive layer 1032 and the second diodegraphitic layer 1034. The third resistive change memory element 1080 isformed by a third nonvolatile CNT resistive block switch in a seriesconnection with a third carbon based diode configured as a Schottkydiode. The third nonvolatile CNT resistive block switch is formed by thethird bottom metal layer 1021, the third switch nanotube fabric layer1023, and the third top metal layer 1025. The third carbon based diodeis formed by the third conductive layer 1011 and the third diodegraphitic layer 1013. The fourth resistive change memory element 1090 isformed by a fourth nonvolatile CNT resistive block switch in a seriesconnection with a fourth carbon based diode configured as Schottkydiode. The fourth nonvolatile CNT resistive block switch is formed bythe fourth bottom metal layer 1041, the fourth switch nanotube fabriclayer 1043, and the fourth top metal layer 1045. The fourth carbon baseddiode is formed by the fourth conductive layer 1031 and the fourth diodegraphitic layer 1033. The first common wiring layer 1004 can operate asa common wordline for the first resistive change memory element 1060 andthe third resistive change memory element 1080. The second common wiringlayer 1005 can operate as a common wordline for the second resistivechange memory element 1070 and the fourth resistive change memoryelement 1090.

Although not shown in FIG. 10B, the first resistive change memoryelement 1060, the second resistive change memory element 1070, the thirdresistive change memory element 1080, and the fourth resistive changememory element 1090 can have nonvolatile graphitic resistive blockswitches formed in place of the nonvolatile CNT resistive blockswitches. The nonvolatile graphitic resistive block switches can beformed by depositing switch graphitic layers in place of the switchnanotube fabric layers. The switch graphitic layers can be formed usingany of the processing methods and techniques used to form the switchgraphitic layer 544, as discussed in detail above. Further, the firstresistive change memory element 1060, the second resistive change memoryelement 1070, the third resistive change memory element 1080, and thefourth resistive change memory element 1090 can have carbon based diodesconfigured as pn junction diodes formed in place of the carbon baseddiodes configured as Schottky diodes. The carbon based diodes configuredas pn junction diodes can be formed by depositing diode graphitic layersin place of the conductive layers.

FIG. 11A illustrates a single-level nonvolatile resistive change memory1100 that can be fabricated in a similar manner to the single-levelnonvolatile resistive change memory 800 shown in FIG. 8F and discussedin detail above. However, the fabrication process for the single-levelnonvolatile resistive change memory 1100 deposits a diode buckyballlayer in place of the diode nanotube fabric layer deposited for thesingle-level nonvolatile resistive change memory 800. The diodebuckyball layer can be formed using any of the processing methods andtechniques used to form the diode buckyball layer 614, as discussed indetail above. The single-level nonvolatile resistive change memory 1100is formed by a bottom wiring layer 1102, an insulating layer 1103, afirst conductive layer 1112, a second conductive layer 1132, a firstdiode buckyball layer 1114, a second diode buckyball layer 1134, a firstbottom metal layer 1122, a second bottom metal layer 1142, a firstswitch nanotube fabric layer 1124, a second switch nanotube fabric layer1144, a first top metal layer 1126, a second top metal layer 1146, adielectric fill for sidewall passivation 1150, a dielectric fill betweenthe stacks 1152, a first common wiring layer 1104, and a second commonwiring layer 1105.

The single-level nonvolatile resistive change memory 1100 illustrated inFIG. 11A has a first resistive change memory element 1160 and a secondresistive change memory element 1170. The first resistive change memoryelement 1160 is formed by a first nonvolatile CNT resistive block switchin a series connection with a first carbon based diode configured as aSchottky diode. The first nonvolatile CNT resistive block switch isformed by the first bottom metal layer 1122, the first switch nanotubefabric layer 1124, and the first top metal layer 1126. The first carbonbased diode is formed by the first conductive layer 1112 and the firstdiode buckyball layer 1114. The second resistive change memory element1170 is formed by a second nonvolatile CNT resistive block switch in aseries connection with a second carbon based diode configured as aSchottky diode. The second nonvolatile CNT resistive block switch isformed by the second bottom metal layer 1142, the second switch nanotubefabric layer 1144, and the second top metal layer 1146. The secondcarbon based diode is formed by the second conductive layer 1132 and thesecond diode buckyball layer 1134.

Although not shown in FIG. 11A, the first resistive change memoryelement 1160 and the second resistive change memory element 1170 canhave nonvolatile buckyball resistive block switches formed in place ofthe nonvolatile CNT resistive block switches. The nonvolatile buckyballresistive block switches can be formed by depositing a switch buckyballlayer in place of the switch nanotube fabric layer. The switch buckyballlayer can be formed using any of the processing methods and techniquesused to form the switch buckyball layer 644, as discussed in detailabove. Further, the first resistive change memory element 1160 and thesecond resistive change memory element 1170 can have carbon based diodesconfigured as pn junction diodes formed in place of the carbon baseddiodes configured as Schottky diodes. The carbon based diodes configuredas pn junction diodes can be formed by depositing buckyball layers inplace of the first conductive layer 1112 and the second conductive layer1132.

FIG. 11B illustrates a multi-level nonvolatile resistive change memory1101 having a third resistive change memory element 1180 and a fourthresistive change memory element 1190 vertically stacked above the firstresistive change memory element 1160 and the second resistive changememory element 1170 of the single-level nonvolatile resistive changememory 1100. The multi-level nonvolatile resistive change memory 1101formed by the bottom wiring layer 1102, the insulating layer 1103, thefirst conductive layer 1112, the second conductive layer 1132, the firstdiode buckyball layer 1114, the second diode buckyball layer 1134, thefirst bottom metal layer 1122, the second bottom metal layer 1142, thefirst switch nanotube fabric layer 1124, the second switch nanotubefabric layer 1144, the first top metal layer 1126, the second top metallayer 1146, the dielectric fill for sidewall passivation 1150, thedielectric fill between the stacks 1152, the first common wiring layer1104, and the second common wiring layer 1105 as discussed in detailabove with respect to the single-level nonvolatile resistive changememory 1100 with like reference numbers representing like elements andcomponents in FIGS. 11A and 11B. The multi-level nonvolatile resistivechange memory 1101 is additionally formed by a thick dielectric layer1154, a third top metal layer 1125, a fourth top metal layer 1145, athird switch nanotube fabric layer 1123, a fourth switch nanotube fabriclayer 1143, a third bottom metal layer 1121, a fourth bottom metal layer1141, a third diode buckyball layer 1113, a fourth diode buckyball layer1133, a third conductive layer 1111, a fourth conductive layer 1131, adielectric fill for sidewall passivation 1151, a dielectric fill betweenthe stacks 1153, and a top wiring layer 1106.

The first resistive change memory element 1160 and the second resistivechange memory element 1170 can be fabricated as discussed in detailabove with respect to the single-level nonvolatile resistive changememory 1100 with like reference numbers representing like elements andcomponents in FIGS. 11A and 11B. The third resistive change memoryelement 1180 and the fourth resistive change memory element 1190 can befabricated in a similar manner to the third resistive change memoryelement 980 and the fourth resistive change memory element 990illustrated in FIG. 9B. However, the fabrication process for the thirdresistive change memory element 1180 and the fourth resistive changememory element 1190 should deposit a diode buckyball layer in place ofthe diode nanotube fabric layer deposited for the third resistive changememory element 980 and the fourth resistive change memory element 990illustrated in FIG. 9B. The diode buckyball layer can be formed usingany of the processing methods and techniques used to form the diodebuckyball layer 614, as discussed in detail above.

The first resistive change memory element 1160 is formed by a firstnonvolatile CNT resistive block switch in a series connection with afirst carbon based diode configured as a Schottky diode. The firstnonvolatile CNT resistive block switch is formed by the first bottommetal layer 1122, the first switch nanotube fabric layer 1124, and thefirst top metal layer 1126. The first carbon based diode is formed bythe first conductive layer 1112 and the first diode buckyball layer1114. The second resistive change memory element 1170 is formed by asecond nonvolatile CNT resistive block switch in a series connectionwith a second carbon based diode configured as a Schottky diode. Thesecond nonvolatile CNT resistive block switch is formed by the secondbottom metal layer 1142, the second switch nanotube fabric layer 1144,and the second top metal layer 1146. The second carbon based diode isformed by the second conductive layer 1132 and the second diodebuckyball layer 1134. The third resistive change memory element 1180 isformed by a third nonvolatile CNT resistive block switch in a seriesconnection with a third carbon based diode configured as a Schottkydiode. The third nonvolatile CNT resistive block switch is formed by thethird bottom metal layer 1121, the third switch nanotube fabric layer1123, and the third top metal layer 1125. The third carbon based diodeis formed by the third conductive layer 1111 and the third diodebuckyball layer 1113. The fourth resistive change memory element 1190 isformed by a fourth nonvolatile CNT resistive block switch in a seriesconnection with a fourth carbon based diode configured as Schottkydiode. The fourth nonvolatile CNT resistive block switch is formed bythe fourth bottom metal layer 1141, the fourth switch nanotube fabriclayer 1143, and the fourth top metal layer 1145. The fourth carbon baseddiode is formed by the fourth conductive layer 1131 and the fourth diodebuckyball layer 1133. The first common wiring layer 1104 can operate asa common wordline for the first resistive change memory element 1160 andthe third resistive change memory element 1180. The second common wiringlayer 1105 can operate as a common wordline for the second resistivechange memory element 1170 and the fourth resistive change memoryelement 1190.

Although not shown in FIG. 11B, the first resistive change memoryelement 1160, the second resistive change memory element 1170, the thirdresistive change memory element 1180, and the fourth resistive changememory element 1190 can have nonvolatile buckyball resistive blockswitches formed in place of the nonvolatile CNT resistive blockswitches. The nonvolatile buckyball resistive block switches can beformed by depositing switch buckyball layers in place of the switchnanotube fabric layers. The switch buckyball layers can be formed usingany of the processing methods and techniques used to form the switchbuckyball layer 644, as discussed in detail above. Further, the firstresistive change memory element 1160, the second resistive change memoryelement 1170, the third resistive change memory element 1180, and thefourth resistive change memory element 1190 can have carbon based diodesconfigured as pn junction diodes formed in place of the carbon baseddiodes configured as Schottky diodes. The carbon based diodes configuredas pn junction diodes can be formed by depositing diode buckyball layersin place of the conductive layers.

Cross Point Memory Arrays with Vertical Columns of Array Line Segments

Prior cross point memory and cell examples, such as those illustratedand described further above with respect to FIGS. 1-12 are formed withapproximately orthogonal array lines representative of word lines andbit lines on horizontal planes, and multiple stacked horizontal planes.However, cross point memory arrays with interconnected vertical columnsof array line segments, bit line segments for example, may also be usedto achieve high density cross point memory arrays.

FIG. 13 illustrates a four layer column cross point cell 1300 with eachlayer in the cell having a pair of bits, for a total of eight bits inthe four layers. In this example, each cell stores information in theform of a resistive state (resistance value). Each cell may store 1 bitof information in the form a low and a high resistance state. Or eachcell may store multiple bits of information with multiple resistancestates. For example two bits of information may be stored with fourresistance states as described in U.S. Pat. No. 8,102,018. Methods offabrication are described further below with respect to FIGS. 16A and16B.

Column cross point cell 1300 is formed on a substrate 1302. Substrate1302 may be formed of a wide range of materials. For example, substrate1302 may be a semiconductor with interconnected devices forming circuitsused in memory operation. Substrate 1302 may be an insulator layer aspart of an integrated circuit, and may include filled via contactsconnecting column cross point cell 1300 with underlying devices andcircuits. Substrate 1302 may also be a ceramic or organic material andmay be rigid or flexible.

Array wire 1304 on the surface of substrate 1302 as illustrated in FIGS.13A-E may be used to interconnect various bit line segments, such bitline segment 1310 with other bit line segments (not shown). Bit linesegment 1310 may be a conductor-filled via for example. Or bit linesegment 1310 may formed with a cylindrical conductive ring on thesidewalls of the via for example. The multiple bit line segments form abit line of a larger array or sub-array region. Bit line segments mayall be connected in parallel, for example, to form a bit line of anarray or sub-array. For example, an array wire orthogonal to the wordlines connects the tops of all bit line segments 1310. For example,referring to FIG. 13C, array wire 1352 may be connected to bit linesegment 1313 at contact 1354. Alternatively, for example, an array wireorthogonal to the word lines connects the bottoms of all bit linesegments 1310. Referring to FIG. 13A, bit line segment 1310 contactsfilled via contact 1306 at contact 1307, which in turn contacts arraywire 1304. However, bit line segments may also be connected in series.For example, the bottom of bit line segment 1310 connected to array wire1304 by filled via contact 1306 may be wired to the bottom of anotherbit line segment (not shown), whose top is connected to another bit line(not shown), and so on, forming a snaking bit line with vertical columnsof bit line segments connected in series in a direction perpendicular tothe word lines.

In a first storage bit plane, word lines 1312-1 and word lines 1312-2contact switch nanotube blocks 1316-1 and 1316-2, respectively, to formend contacts 1320-1 and 1320-2, respectively. Bit line segment 1310contacts switch nanotube blocks 1316-1 and 1316-2 to form end contacts1322-1 and 1322-2, respectively. Protective insulators 1318-1 and 1318-2on the top surface of switch nanotube blocks 1316-1 and 1316-2,respectively, are included as part of the methods of fabricationdescribed further below with respect to FIGS. 16A and 16B. However,these insulators are not required as part of the memory cell operation.NV CNT resistive block switch 1314-1 includes end contact 1320-1 and endcontact 1322-1. NV CNT resistive block switch 1314-2 includes endcontact 1320-2 and end contact 1322-2. Insulators 1308-1 and 1308-2 areused to prevent electrical contact between filled via contact 1306 andswitch nanotube blocks 1316-1 and 1316-2. Storage bit planes areseparated by insulator 1324.

In a second storage bit plane, word lines 1312-3 and word lines 1312-4contact switch nanotube blocks 1316-3 and 1316-4, respectively, to formend contacts 1320-3 and 1320-4, respectively. Bit line segment 1310contacts switch nanotube blocks 1316-3 and 1316-4 to form end contacts1322-3 and 1322-4, respectively. Protective insulators 1318-3 and 1318-4on the top surface of switch nanotube blocks 1316-3 and 1316-4,respectively, are included as part of the methods of fabricationdescribed further below with respect to FIGS. 16A and 16B. However,these insulators are not required as part of the memory cell operation.NV CNT resistive block switch 1314-3 includes end contact 1320-3 and endcontact 1322-3. NV CNT resistive block switch 1314-4 includes endcontact 1320-4 and end contact 1322-4.

In a third storage bit plane, word lines 1312-5 and word lines 1312-6contact switch nanotube blocks 1316-5 and 1316-6, respectively, to formend contacts 1320-5 and 1320-6, respectively. Bit line segment 1310contacts switch nanotube blocks 1316-5 and 1316-6 to form end contacts1322-5 and 1322-6, respectively. Protective insulators 1318-5 and 1318-6on the top surface of switch nanotube blocks 1316-5 and 1316-6,respectively, are included as part of the methods of fabricationdescribed further below with respect to FIGS. 16A and 16B. However,these insulators are not required as part of the memory cell operation.NV CNT resistive block switch 1314-5 includes end contact 1320-5 and endcontact 1322-5. NV CNT resistive block switch 1314-6 includes endcontact 1320-6 and end contact 1322-6.

In a fourth storage bit plane, word lines 1312-7 and word lines 1312-8contact switch nanotube blocks 1316-7 and 1316-8, respectively, to formend contacts 1320-7 and 1320-8, respectively. Bit line segment 1310contacts switch nanotube blocks 1316-7 and 1316-8 to form end contacts1322-7 and 1322-8, respectively. Protective insulators 1318-7 and 1318-8on the top surface of switch nanotube blocks 1316-7 and 1316-8,respectively, are included as part of the methods of fabricationdescribed further below with respect to FIGS. 16A and 16B. However,these insulators are not required as part of the memory cell operation.NV CNT resistive block switch 1314-7 includes end contact 1320-7 and endcontact 1322-7. NV CNT resistive block switch 1314-8 includes endcontact 1320-8 and end contact 1322-8.

In this example, four storage bit planes are illustrated in column crosspoint cell 1300. However, other storage bit planes may be formed usingmethods described further below with respect to FIGS. 16A and 16B. Forexample, 8 bit planes, 16 bit planes, and even more bit planes may beformed.

Referring to FIG. 13B, which is the same as FIG. 13A except for theaddition of diode-forming liner 1311. The sidewalls of via hole 1740formed by etching through top surface 1315, as illustrated further belowin FIG. 17H, may be coated with diode-forming liner 1311 (typicallyformed by using industry ALD process methods and tools), thenconductor-filled (using known industry methods) in contact withdiode-forming liner 1311 and filled via contact 1306 at contact 1307, toform bit line segment 1313 and column cross point cell 1330 illustratedin FIG. 13B. Bit line segment 1313 contacts the inner sidewall ofdiode-forming liner 1311, whose outer sidewall contacts switch nanotubeblocks 1316-1 and 13-16-2 at end contacts 1323-1 and 1323-2,respectively, forming series diodes between bit line segment 1313 andswitch nanotube blocks 1316-1 and 1316-2. Series diodes are also formedbetween bit line segment 1313 and switch nanotube blocks 1316-3, 1316-4,1316-5, 1316-6, 1316-7, and 1316-8.

FIG. 13C illustrates column cross point cell 1350, which is similar tocolumn cross point cell 1330 shown in FIG. 13B, except that array wire1352 is formed on top surface 1315 (FIG. 13B). When forming cross pointcell 1350, array wire 1304, filled via contact 1306, and insulators1308-1 and 1308-2, illustrated in FIG. 13A, may be omitted as describedby methods 1610 and array wire 1352 may be formed by methods 1680 asshown in methods flow chart 1600 illustrated in FIGS. 16A and 16B.

Measurements of uncorrelated (that is, unaligned) fabrics illustrated inFIG. 12A and correlated (that is, aligned) fabrics illustrated in FIG.12B result in differences in sheet resistance values as measured usingknown four-point measurement techniques. A CNT fabric was deposited on awafer forming an uncorrelated fabric layer and the sheet resistance wasmeasured. Then this CNT fabric layer was processed with mechanicalpressure alignment methods similar to those described further above withrespect to FIGS. 12A and 12B and also in U.S. patent application Ser.No. 13/076,152, and sheet resistance was again measured using four-pointprobe measurements. These sheet resistance measurements showed that thesheet resistance of ordered CNT fabrics was at least 2× larger than forunordered CNT fabrics.

FIG. 13D is the same as FIG. 13C, except that the switch nanotube blocks1316-1, 1316-2, 1316-3, 1316-4, 1316-5, 1316-6, 1316-7, and 1316-8 havebeen replaced by switch nanotube blocks 1366-1, 1366-2, 1366-3, 1366-4,1366-5, 1366-6, 1366-7, and 1366-8, respectively, to form column crosspoint cell 1360 as illustrated in FIG. 13D using ordered CNT fabrics. Inthis example, CNTs in the ordered CNT fabric are approximately alignedin the direction of word lines 1312-1, 1312-2, 1312-3, 1312-4, 1312-5,1312-6, 1312-7, and 1312-8 and may be formed by methods 1620 illustratedin FIG. 16A and methods described further above with respect to FIG.16B. However, CNTs may be aligned approximately parallel to array wire1352, or may be approximately aligned in any direction between parallelto word lines and parallel to array wires, which are orthogonal to wordlines. CNT alignment may be used to modulate switch nanotube blockresistance as described further above. Switch nanotube blocks may alsobe formed by layers of both unaligned and aligned CNT fabrics as well.

FIG. 13E is the same as FIG. 13D, except that the switch nanotube blocks1366-1, 1366-2, 1366-3, 1366-4, 1366-5, 1366-6, 1366-7, and 1366-8 havebeen replaced by switch nanotube blocks 1386-1, 1386-2, 1386-3, 1386-4,1386-5, 1386-6, 1386-7, and 1386-8, respectively, to form column crosspoint cell 1380 as illustrated in FIG. 13E using ordered coated CNTfabrics. In this example, coated CNTs in the ordered coated CNT fabricare approximately aligned in the direction of word lines 1312-1, 1312-2,1312-3, 1312-4, 1312-5, 1312-6, 1312-7, and 1312-8 and may be formed bymethods 1620 illustrated in FIG. 16A and methods described further abovewith respect to FIG. 16B. However, coated CNTs may be aligned parallelto array wire 1352, or may be aligned in any direction between parallelto word lines and parallel to array wires. Coated CNTs may be used toform unaligned CNT fabrics. The coating may be used to modulate switchnanotube block resistance by introducing an insulating layer such assilica between the CNTs in the coated CNT layer thereby increasing theswitch nanotube block resistance. CNTs may also be functionalized asdescribed further above with respect to FIGS. 4C, 4D, and 4E. Switchnanotube blocks may also be formed by layers of unaligned and aligned,coated and uncoated, and functionalized and non-functionalized CNTfabrics as well.

In addition to the various switch nanotube blocks described in FIGS.13A-13E, the switch nanotube blocks illustrated in FIGS. 13A-13E may bereplaced by switch graphitic blocks corresponding to switch graphiticblock 168 illustrated in FIG. 1D. Also, the switch nanotube blocksillustrated in FIGS. 13A-13E may be replaced by switch buckyball blockscorresponding to switch buckyball block 188 illustrated in FIG. 1E byadapting methods 1620 illustrated in FIG. 16A for deposition andpatterning of graphitic layers and buckyball layers.

FIG. 14 illustrates NV CNT resistive block switch 1401 including switchnanotube block 1416 on insulator 1408 which is supported by substrate1402. Protective insulator 1418 is in contact with the top surface ofswitch nanotube block 1416. Contacts 1411 and 1412 formed adjacent tothe end regions of switch nanotube block 1416 form end contacts 1421 and1422, respectively, separated by a distance of 250 nm. In this example,contacts 1411 and 1412 were formed of TiPd. However, they may instead beformed using a wide variety of contact materials such as conductors,semiconductors, carbon nanotubes, various nanowires, and other materialsas described further below with respect to FIG. 17A. Contact 1411corresponds to any of the word lines illustrated in FIGS. 13A-13E, suchas word line 1312-2 for example. Contact 1412 corresponds to bit linesegment 1310. End contact 1421 corresponds to any of the end contacts toword lines in FIG. 13, such as end contact 1320-2 for example. Endcontact 1422 corresponds to any of the end contacts to bit line segment1310, end contract 1322-2 for example. NV CNT resistive block switch1401 is described in U.S. Patent Pub. No. 2008/0160734.

In operation, test results of individual NV CNT resistive block switches1401 are illustrated by graph 1500 shown in FIG. 15, and also describedin U.S. Patent Pub. No. 2008/0160734. READ-SET-READ-RESET-READ-SET-etc.operations are performed and nonvolatile low resistance SET state values1510 and nonvolatile high resistance RESET state values 1520 aremeasured and plotted. Low resistance SET states 1510 show a lowresistance range of 20 kΩ to 100 kΩ, with two points at 500 kΩ. Tighterlow resistance SET state value spreads are observed after several tensof cycles. High resistance RESET state values in excess of 100 MΩ, and200 MΩ in most cases, were measured. The ratio of the lowest value ofhigh resistance RESET state value to the highest value of the lowresistance SET value is 200:1 (ratio=100 MΩ/0.5 MΩ). SET and RESEToperations were performed with a single pulse; however, multiple pulsesmay be used as well for finer control of low and high resistance statevalues. As described in U.S. Patent Pub. No. 2008/0160734, variouscombinations of pairs of contacts to switch nanotube block surfaces,such as switch nanotube block 1416, may be formed including a topcontact and a side contact; contacts fully or partially contactingswitch nanotube block surfaces, and other combinations used to form NVCNT resistive block switches. NV CNT resistive block switch 1401, andvariations thereof, may be used in any memory architecture; for example,in column cross point cell 1300 illustrated in FIGS. 13A-13E.

Methods of Fabrication and Structures of Cross Point Memory ArraysFormed with Vertical Columns of Array Line Segments

Methods (of fabrication) flow chart 1600 illustrated in FIGS. 16A and16B describes methods (processes) of forming the structures illustratedin FIGS. 17A-17I. Variations to methods of fabrication 1600 such as theaddition or omission of steps and varying the order of steps are stillwithin the scope described below with respect to FIGS. 16 and 17.

Methods 1610 assumes that substrate 1302 illustrated in FIG. 17Aincludes many of the components of n-type and p-type field effectdevices (MOSFETs) with drain, source, and gate nodes andinterconnections to form circuits (typically CMOS circuits) in supportof the memory function to be fabricated on the surface of substrate1302. Further, connections between memory arrays and sub-arrays formedon the surface of substrate 1302 and circuits are present withinsubstrate 1302.

Methods 1610 deposit a conductor layer on the surface of substrate 1302illustrated in structure 1700 shown in FIG. 17A using known industrymethods, or methods described further below in the case of nanotubefabrics for example. Thicknesses may range from 5 nm to 500 nm forexample. The term conductor may include metals, metal alloys,semiconductors, silicides, conductive oxides, various allotropes ofcarbon, and other materials. The following are examples of conductors,conductive alloys, and conductive oxides: Al, Al(Cu), Ag, Au, Bi, Ca,Co, CoSi_(x), Cr, Cu, Fe, In, Ir, Mg, Mo, MoSi₂, Na, Ni, NiSi_(x), Os,Pb, PbSn, PbIn, Pd, Pd₂Si, Pt, PtSi_(x), Rh, RhSi, Ru, RuO, Sb, Sn, Ta,TaN, Ti, TiN, TiAu, TiCu, TiPd, TiSi_(x), TiW, W, WSi₂, Zn, ZrSi₂, andothers for example.

The following are examples of semiconductors that may be used asconductors: Si (doped and undoped), Ge, SiC, GaP, GaAs, GaSb, InP, InAs,InSb, ZnS, ZnSe, CdS, CdSe, CdTe, GaN, and other examples.

Various allotropes of carbon may also be used as conductors such as:amorphous carbon (aC), carbon nanotubes such as nanotube fabrics,graphene, buckyballs, and other examples.

In addition to the materials described further above such conductors,semiconductors, conductive oxides, and allotropes of carbon, nanowiresformed of various conductor, semiconductor, and conductive oxidematerials, such as those described further above, may also be used aswell.

Next, methods 1610 deposit a resist layer, expose and develop theresist, and etch to pattern array wires on the surface of substrate 1302using known industry methods, forming array wire 1304 as illustrated inFIG. 17A. Array wire 1304 width may vary over a large range; forexample, F may be scaled over a large range: on the order of 250 nm toon the order of 10 nm.

Next, methods 1610 deposit an insulating layer 1702 using known industrymethods to a thickness of 5 to 500 nm for example. Examples ofinsulators are SiO₂, SiN, Al₂O₃, TEOS, polyimide, HfO₂, TaO₅,combinations of these insulator materials, and other insulatormaterials.

Then, methods 1610 etch via holes in the insulating layer 1702 to thetop surface of array wire 1304 using known industry methods. Then, aconductive layer is deposited filling the via hole. The combinedstructure is planarized using known industry (e.g. CMP) methods, leavingthe surface of filled via contacts 1306 exposed. The formation ofinsulator 1702 and filled via contact 1306 is complete in this step.

Then, methods 1610 deposit insulator layer 1704 on the top surface ofinsulator 1702 and the top surface of filled via contact 1306 in athickness range of 1 nm to 500 nm as needed. Insulator layer 1704 isformed to prevent the subsequent CNT layer deposition from electricallycontacting the surface of filled via contacts 1306. Insulator 1704 maybe formed of SiN for example. However, insulator 1704 may also be formedwith SiO₂, Al₂O₃, TEOS, polyimide, HfO₂, TaO₅, combinations of theseinsulator materials, and other insulator materials. At this point in theprocess, structure 1700 illustrated in FIG. 17A is complete.

Next, methods 1620 deposit a CNT layer, or several CNT layers, asillustrated in structure 1705 shown in FIG. 17B, to form a porousunordered nanotube (CNT) fabric layer 1706 of matted carbon nanotubes.An unordered nanotube fabric layer deposited on a substrate element isshown by the scanning electron microscope (SEM) image 1200 in FIG. 12A.This may be done with spin-on technique or other appropriate techniqueas described in U.S. Pat. Nos. 6,643,165, 6,574,130, 6,919,592,6,911,682, 6,784,028, 6,706,402, 6,835,591, 7,560,136, 7,566,478,7,335,395, 7,259,410 and 6,924,538, and U.S. Patent Pub. No.2009/0087630, the contents of which are hereby incorporated by referencein their entireties (hereinafter and hereinbefore, the “incorporatedpatent references”). Under preferred embodiments, the carbon nanotubelayer may have a thickness of approximately 0.5-500 nm for example. TheCNT layer may be formed of multiwalled nanotubes, single wall nanotubes,metallic nanotubes, semiconductor nanotubes, and various combinations ofall nanotube types, doped and functionalized as described in more detailin U.S. patent application Ser. No. 12/356,447 and U.S. patentapplication Ser. No. 12/874,501, herein incorporated by reference intheir entirety.

Alternatively, methods 1620 may, after the deposition of one or more CNTlayers such as described further above, use mechanical or other methodsto approximately align some or most of the nanotubes in a preferreddirection to form an ordered nanotube fabric layer, or several orderednanotube layers, as described in U.S. Patent App. No. 61/319,034.Ordered nanotube fabrics may be ordered throughout the nanotube fabricthickness. However, ordered nanotube fabrics may be present for only aportion of the nanotube fabric thickness, while the rest of the nanotubefabric remains an unordered fabric. Ordered and unordered nanotubefabrics may be present in multiple layers that form nanotube fabriclayer 1706. FIG. 12B illustrates a scanning electron microscope (SEM)image 1250 of an ordered nanotube fabric.

Next, insulator layer 1708 is deposited over nanotube fabric layer 1706in a thickness range of 1 nm to 500 nm as needed. This insulator layermay be formed of SiN for example. However, the insulator layer may alsobe formed using SiO₂, Al₂O₃, TEOS, polyimide, HfO₂, TaO₅, combinationsof these insulator materials, and other insulator materials.

Then, methods 1620 deposit, expose, and develop a resist layer on thesurface of insulator 1708. If nanotube fabric layer 1706 is an unorderednanotube fabric layer (FIG. 12A), the resist layer images may have anyorientation with respect to the nanotube fabric layer.

However, referring to column cross point cell 1300 in FIGS. 13A-13E andend contacts 1320-1 and 1322-1 of switch nanotube block 1316-1 forexample, if nanotube fabric 1706 is a fully or partially orderednanotube fabric (FIG. 12B), then the orientation of the resist imageswith respect to the orientation of CNTs in nanotube fabric 1706 may beimportant to the electrical operation of NV CNT resistive blockswitches, such as NV CNT resistive block switch 1314-1.

For example, if CNTs in nanotube fabric layer 1706 are ordered (FIG.12B), then resist images may be aligned relative to the preferred CNTdirection such that the CNTs in nanotube fabric layer 1706 areapproximately orthogonal to end contacts 1320-1 and 1322-1 when formedlater in the process. Alternatively, resist images may be alignedrelative to the preferred CNT direction such that the CNTs in nanotubefabric layer 1706 are approximately parallel to end contacts 1320-1 and1322-1 when formed later in the process. In still another alternative,resist images may be aligned relative to the preferred CNT directionsuch that the CNTs in nanotube fabric layer 1706 are approximatelypositioned at any desired angle relative to end contacts 1320-1 and1322-1 when formed later in the process. For ordered nanotube fabrics,the desired angles for CNTs in nanotube fabric layer 1706 may bedetermined by building test devices, such as NV CNT resistive blockswitch 1400 illustrated in FIG. 14, and then electrically testing suchdevices as illustrated by graph 1500 in FIG. 15. CNT orientations withrespect to end contacts may depend on the intended applications. For NVCNT resistive block switches, such as NV CNT resistive block switch1314-1, for example, used in column cross point cell 1300 (FIG. 13A),achieving NV high resistance states for both high and low resistancevalues, with a high resistance state-to-low resistance state ratiogreater than 2:1 is needed, as described further above with respect toFIGS. 3A and 3B. At this point in the process, structure 1705illustrated in FIG. 17B is complete.

Then, with developed lithographic images formed on the surface ofinsulator 1708, methods 1620 etch insulator layer 1708 using industrystandard methods and etch underlying nanotube fabric layer 1706 using anoxygen plasma, for example, resulting in protective insulator 1714 andnanotube fabric 1712 illustrated by structure 1710 shown in FIG. 17C. Atthis point in the process, structure 1710 illustrated in FIG. 17C iscomplete.

Next, methods 1630 deposit a conductive layer on the surfaces ofinsulator 1704, protective insulator 1714, and the approximatelyvertical sidewalls of nanotube fabric 1712. This conductive layer may beformed using conductors, semiconductors, and various allotropes ofcarbon, and other materials as described further above with respect tothe conductive layer deposited on the surface of substrate 1302illustrated in FIG. 17A.

Next, methods 1630 planarize the conductive layer (e.g. CMP) leaving thetop surface of protective insulator 1714 exposed using known industrymethods. Then, methods 1630 form a resist layer on the surface of theplanarized conductive layer using known industry methods. Then, methods1630 etch the planarized conductive layer forming a first word linelevel including word lines 1312-1 and 1312-2 with end contacts 1711 and1713, respectively, to nanotube fabric 1712 as illustrated in FIG. 17D.At this point in the process, structure 1715 illustrated in FIG. 17D iscomplete.

Next, methods 1630 deposit and planarize an insulator layer using knownindustry methods. This insulator layer may be formed of SiO₂ forexample. However, the insulator layer may also be formed using SiN₂,Al₂O₃, TEOS, polyimide, HfO₂, TaO₅, combinations of these insulatormaterials, and other insulator materials. At this point in the process,structure 1720 illustrated in FIG. 17E is complete.

Next, methods 1640 form insulator layer 1728 and nanotube fabric layer1726 illustrated in structure 1725 illustrated in FIG. 17F,corresponding to dielectric layer 1708 and nanotube fabric layer 1706,respectively in FIG. 17B. Methods 1640 correspond to methods 1620described further above. At this point in the process, structure 1725illustrated in FIG. 17F is complete.

Next, methods 1650 form a second word line level with protectiveinsulator 1734 and word lines 1312-3 and 1312-4 with end contacts 1731and 1733, respectively, to nanotube fabric 1732 as illustrated in FIG.17G. Word lines 1312-3 and 1312-4 correspond to word lines 1312-1 and1312-2 illustrated in FIG. 17D; end contacts 1731 and 1733 correspond toend contacts 1711 and 1713, respectively illustrated in FIG. 17D;nanotube fabric 1732 corresponds to nanotube fabric 1712 illustrated inFIG. 17D; and protective insulator 1734 corresponds to protectiveinsulator 1714 illustrated in FIG. 17D.

Then, methods 1650 form insulator layer 1729, corresponding to insulatorlayer 1722 illustrated in FIG. 17E. Methods 1650 correspond to methods1630 described further above. At this point in the process, structure1730 illustrated in FIG. 17G is complete.

Next, methods 1660 form additional N−2 word line levels beginning on thetop surface of insulator 1729 illustrated by structure 1730 in FIG. 17Gby repeating methods 1640 and 1650 N−2 times. In this example, there arefour word line levels corresponding to N=4. Structure 1735 illustratedin FIG. 17H shows four word line levels with insulator 1724.

Next, methods 1670 form resist images on the top surface of insulator1724 with a hole in the resist image centered approximately mid-waybetween the inner edges of the underlying word lines. Then, methods 1670etch through insulator, protective insulator, nanotube fabric layers,and insulator 1704 to the top surface of via hole contact 1306 usingindustry processes to form via hole 1740 illustrated by structure 1735shown in FIG. 17H. For nanotube fabrics, an oxygen plasma etch may beused. After etching, insulator 1704 is cut into two parts, insulators1308-1 and 1308-2. At this point in the process, structure 1735illustrated in FIG. 17H is complete.

Optionally, at this point in the process flow, methods 1680 may depositdiode-forming liner 1311 on the sidewalls of via hole 1740 using knownindustry methods, ALD deposition for example. Diode forming liner 1311may be semiconducting, metallic, conductive oxide or nitride, carbon,and other material. Diode-forming liner 1311 may be formed with a singlelayer or two or more layers of various materials. At this point in theprocess, structure 1750 illustrated in FIG. 17I is complete.

Next, methods 1680 deposit a conductive layer on top surface ofinsulator 1724 filling via hole 1740. Alternatively, methods 1680 maydeposit a conformal layer on the walls of via hole 1740 for purposes offorming a preferred contact with switch nanotube blocks. Preferredcontacts may be used to enhance NV CNT resistive block switchperformance by forming linear contacts or non-linear contacts such asSchottky diodes for example. Then, methods 1680 deposit a conductivelayer on the top surface of the conformal layer filling the via hole1740.

Next, the top surface is planarized to the top surface of insulator1724. At this point in the process, bit line segment 1310 in columncross point cell 1300 illustrated and described further above withrespect to FIGS. 13A and 13B is complete for column cross point cellswith array wire 1304 below the array structure.

However, for column cross point cells with array wire 1352 above thearray structure, optional steps in methods 1610 are omitted. Thenmethods 1680 deposit and pattern a conductive layer in contact with theexposed top surface of bit line segments 1313 forming array lines 1352.Array lines 1352 contact bit line segments 1313 at contacts 1354 asshown in FIGS. 13C-13E. Array wire 1352 may, but need not, contact thetop surface of diode-forming liner 1311. Also, while FIGS. 14A and 14Bshow array wires 1304 below the array and FIGS. 14C-14E show array wires1352 above the array, each of the figures may be formed with array wiresbelow the array or above the array.

Variations to methods of fabrication 1600 such as the addition oromission of steps and varying the order of steps are still within thescope described above with respect to FIGS. 16 and 17 and may be used toform diodes in series with switch nanotube blocks. For example,referring to FIG. 13A, a diode may be formed in contact with word line1312-2 and switch nanotube block 1316-2 at end contact location 1320-2,with a near-Ohmic contact at end contact 1322-2 between switch nanotubeblock 1316-2 and bit line segment 1310. Alternatively, a diode may beformed in diode liner 1311 in contact with bit line segment 1310 andswitch nanotube block 1316-2 at end contact location 1322-2, with anear-Ohmic contact at end contact 1320-2 between switch nanotube block1316-2 and word line 1312-2 as illustrated in FIG. 13B. Combinations ofdiode and near-ohmic contact described further above may be formed forall bit locations in column cross point cell 1300.

Size and Performance of Cross Point Memory Arrays

There are two memory tracks: volatile memory (mostly DRAM at nanosecondspeed) and nonvolatile memory (mostly NAND Flash at microsecond speed).However, there is a strong desire by memory users for memory functionsthat are: nonvolatile (NV), fast (nanosecond), low power, with highendurance, and low cost for applications as diverse as cell phones andhigh speed computers as shown by chart 1800 as illustrated in FIG. 18.Chart 1800 shows various examples of nonvolatile random access memories(NV RAMs) for use in various applications. In these various examples,the nonvolatile memories may have different architectures for thedifferent applications. However, all are formed using CNT-based, orgraphitic-based, or buckyball-based, or combinations thereof, crosspoint memory arrays and may use nonvolatile cross point cellsillustrated further above in FIGS. 1, 4, 5, 6, 7, 8, 9, 10, 11, and 13.

NV RAM 1810 refers to Gigabyte-to-Terabyte nonvolatile memory functionsformed with Gigabit (Gb)-to-Terabit (Tb) NV NRAM chips with nanosecond(ns) performance. NV RAM 1820 is an example of an embedded Gigabit,nanosecond, and nonvolatile memory with logic circuits on the same chipto form a microcontroller function. IBM and other industry leaders haveidentified a new memory category (architecture) referred to as StorageClass Memory (SCM) also with an objective of nonvolatile operation,gigabyte-to-terabyte size, with nanosecond performance, high endurance,and low cost as illustrated by SCM memory 1830. SCM memory 1830 isformed with Gb—Tb chips of NV RAM-based nanosecond memory as are NV RAMs1810 and 1820. However, SCM memory 1830 is architected as part of amemory hierarchy that interfaces between a smaller volatile RAMoperating at nanosecond speed and a larger solid state drive (SSD) 1840operating at microsecond speed. And also, there is a need to increasenonvolatile solid state drive (SSD) 1840 capacity to Terabyte size atmicrosecond performance. The memory size and performance requirementsdetermines the underlying cross point cell configurations used to meetthe requirements of NV RAMs 1810 and 1820 and those of SCM memory 1830and SSD 1840 as described further below. Numerous other applications arepossible (not shown).

Very low contamination and particulate levels achieved in CNT fabricshave enabled Nantero, Inc. to develop reproducible NV CNT switches asnonvolatile resistive storage devices (FIG. 1A) in functioning 4 Mb NRAMchips, with underlying CMOS circuits, that have been tested forfunctionality and performance as summarized in table 1900 illustrated inFIG. 19 further below. 4 Mb NRAM arrays are formed by interconnectingnonvolatile cells, such as resistive memory cell 100 illustrated in FIG.1A. Discrete NV CNT switch test sites have led to an understanding ofthe inherently fast CNT fabric switching behavior as described furtherbelow with respect to FIG. 20. 4 Mb NRAM chips have been made in variousfabricators operating at technology nodes in the 45 to 250 nm range.

The electrical characteristics shown in table 1900, illustrated in FIG.19, are from 4 Mb NRAM chips with arrays formed with resistive memorycell 100 (FIG. 1A) and sorted for high performance operation. Operatingspeeds of 20 ns for SET (program) and RESET (erase) write operations areexceptionally fast for nonvolatile devices. SET, RESET, and READoperating speeds are primarily determined by the resistance of the NVCNT switch and array capacitances. The switching mechanisms themselveswithin the CNT device are much faster, picoseconds for example. Theemphasis has also been on wide and robust operating margins, with hightemperature operation and data retention, and high endurance asillustrated in table 1900. These NV CNT switches are operated so thathigh resistance and low resistance states are separated by at least100×, and often up to 1,000×, corresponding to READ currents at 1 Volthaving SET/RESET ratios of 10 μA/0.1 μA and 10 μA/0.01 μA, respectively.A 10 μA current at 1 V corresponds to a low resistance SET state of 100kΩ, and currents in the 0.01-0.1 μA range at 1 V correspond to highresistance RESET states in the 10-100 MΩ range. NV CNT resistive blockswitch 104 (FIG. 1A) may be operated in bidirectional and/orunidirectional mode. The wide separation between high and lownonvolatile resistance states stored in NV CNT resistive block switch104 (FIG. 1A) enables a large resistance (current) exclusion (buffer)zone for achieving the operational integrity needed for high volumeproduction. The 100-1000× high-to-low resistance ratio enables storageof multiple (two or more) resistance state for multi-bit storage in eachNV CNT resistive block switch 104. For example, two resistive statesstore 1 bit of data, four resistive states store 2 bits of data, andso-on, as described in U.S. Pat. No. 8,102,018.

CNT fabric switching is inherently high speed as explained with respectto CNT switch characteristics 2000 illustrated in FIG. 20, which is anelectrical representation of NV CNT resistive block switch 104illustrated in FIG. 1A, which includes switch nanotube block 108 incontact with a bottom electrode, first conductive terminal 106, and atop electrode, second conductive terminal 110. Switch nanotube block 108is formed using one, or several, patterned CNT fabric layers between topand bottom electrodes. Measurements of millions of these switches showthat nonvolatile resistance state values depend on applied voltages andcurrents and are a function of the number and state of a combination ofmultiple series and parallel nanoscopic switches formed by pairs of CNTsin the porous CNT fabric. CNT pairs 2020 form individual nanoscopicswitches that may be in electrical contact in contact region 2030representing a SET (ON) or “1” state, and shown schematically inschematic 2040, or may be separated representing a RESET (OFF) or “0”state and also shown schematically in schematic 2040. Schematic 2040includes: multiple closed nanoscopic switches 2050, open nanoscopicswitches 2060, and resistors 2070 in series and parallel combinations.In this example, there are two electrical paths formed between top andbottom electrodes. A first electrical path is between nodes 1 and 2, anda second electrical path is between nodes 3 and 4. Physical CNT pair2020 separation in an OFF state may be in the range of 1-2 nm, so theinertia associated with nanoscopic switching of CNT pairs between ON andOFF states is very small enabling nanoscopic contact closing and openingat picosecond speeds. Table 2080 summarizes SET and RESET write modes,resulting low and high resistance states, respectively, andcorresponding electrostatic and phonon-driven switching, respectively.The NV CNT resistive block switch 104 capacitance is very low, typicallyin the atto-Farad (aF) range (10⁻¹⁸ F), because of the porosity of theCNT fabric and the separation of the top and bottom electrodes. NV CNTswitches may be operated in combinations of bidirectional andunidirectional operating modes. While electrical characteristics andswitching speeds have been described further above with respect to NVCNT resistive block switches 104 and 142 illustrated in FIGS. 1A and 1C,respectively, it is reasonable to expect similar electricalcharacteristics and switching speeds from resistive block switchesformed with other allotropes of carbon such NV graphitic resistive blockswitches 162 and NV buckyball resistive block switches 182 illustratedin FIGS. 1D and 1E, respectively.

NV RAM cells that include a MOSFET select device, such as resistivememory cell 100 illustrated in FIG. 1A, cannot be scaled to sufficientlysmall dimensions to meet computing needs described with respect to chart1800 illustrated in FIG. 18. What is needed for these applications aremuch smaller nonvolatile cells retaining the inherent nonvolatile highspeed electrical switching characteristics of CNT fabrics described withrespect to FIG. 20 and demonstrated with respect to 4 Mb NRAM chips asdescribed further above with respect to FIG. 19. What is needed are newCNT fabric-based devices that perform both select and storage functionsfor use in 1-R resistive cross point cells for the 15 nm technology nodein the examples described further below, but scalable to sub-10 nmdimensions. 1-R cross point cells are compatible with 100Gbit-to-Terabit size memory chips. Such large memory functions formedwith 1-R cross point switches require minimizing or eliminating thecross point array parasitic currents and data disturb limitationsdescribed further above with respect to FIG. 2A. Nanosecond speedrequirements make 1-R cross point cell operation even more difficult asdescribed further below with respect to nanoscale material andstructural innovations for nanosecond performance, terabit scale memorychips.

At this point in the present disclosure, by way of example, an estimateis made of the physical size of a cross point array-based memory of 1terabit using NV CNT resistive block switches similar to those used toform cells in cross point array 120 shown in FIG. 1B. Such NV CNTresistive block switches may be formed with switch nanotube blockssimilar to switch nanotube block 372 illustrated in FIG. 3D, forexample, with dimensions F=15 nm corresponding to a 15 nm technologynode. Cross point arrays have a periodicity of 2F so the cell area is4F² as illustrated in FIG. 1B. For F=15 nm, cross point array cell is 30nm by 30 nm, with an area=900 nm².

In this example, the 1 terabit (10¹² bits) memory is formed with 10,000cross point sub-arrays, each cross point sub-array having 100 megabits(10⁸ bits). Cross point array requirements 320 are illustrated in FIG.3B. Curve 325, a linear log-log plot illustrated in FIG. 3B, shows thecorresponding relationship between the minimum required value of R_(ON)as a function of the maximum number of cells in a cross point array.Curve 325 may be used to estimate the minimum R_(ON) resistance requiredfor a 10⁸ cell cross point array as follows. Based on I-V curve 300illustrated in FIG. 3A the minimum measured R_(ON) value for NV CNTresistive block switch 104 (FIG. 1A) is R_(ON)=10⁶Ω; that is R_(ON)=1MΩ. From curve 325 illustrated in FIG. 3B, a minimum R_(ON) value of 1MΩ (point 330) corresponds to a maximum number of cells in cross pointarrays using NV CNT resistive block switches 104 (FIG. 1A) of 4×10⁵(point 340). For a cross point array of 10⁸ bits, a NV CNT resistiveblock switch of higher resistance is required to increase the maximumnumber of cells in a cross point array by 250 times, from 4×10⁵ cells(point 340) to a sub-array size of 10⁸ cells. From a section of linearlog-log curve 325, an estimated increase in the number of cells by 100times (100×), from 10³ to 10⁵ cells, corresponds to an increase in therequired R_(ON) by approximately 40×, from corresponding R_(ON) valuesof 10⁴ to 4×10⁵Ω. Scaling for an increase in the number of cells by250×, from 4×10⁵ cells (point 340) to 10⁸ cells, the resistance valueneeds to increase by an additional 2.5× more than the 40×R_(ON)resistance increase corresponding to a 100× increase in the number ofcells. That is, an increase in the number of cross point sub-array cellsby 250× to 10⁸ cells requires an R_(ON) resistance increase of 100×.Since a cross point array of 4×10⁵ bits (point 340) corresponds to anR_(ON) resistance of 1 MΩ (point 330), then the R_(ON) resistance for asub-array of 10⁸ bits is 100×1 MΩ or a minimum R_(ON) value of 100 MΩ.

FIG. 21 illustrates a schematic representation of a cross point memoryarray 2100 formed with multiple cross point sub-arrays 2120. In thisexample, cross point memory array 2100 is configured as a 1 terabit (1Tb) cross point memory array with 10,000 cross point sub-arrays 2120,each sub-array corresponding to cross point array 120 illustrated inFIG. 1B, and each sub-array having 100 megabits (100 Mb). In thisexample, cross point sub-arrays 2120 may be formed with 10,000 bitsalong the X-direction array wire 2125 and 10,000 bits in the Y-directionalong array wire 2130, in an approximately square configuration.However, cross point sub-array 2120 may also be formed in other 100 Mbconfigurations, rectangular for example, with an unequal number of cellson array wires 2125 and 2530. By way of example, 20,000 cells alongarray wire 2125 and 5,000 cells along array wire 2130. Cross pointsub-arrays 2120 may be laid out in equal number in horizontal andvertical directions to form a square 1 Tb cross point memory array 2100.Alternatively, 1 Tb cross point memory array 2100 may be implemented inother memory array configurations, such as with rectangular arrayconfigurations for example.

In this example, each cross point sub-array 2120 cell has a horizontalcell pitch of 2F=30 nm. Therefore, cross point sub-array 2120 has ahorizontal physical dimension X=300 μm formed by 10,000 cells ofperiodicity 2F=30 nm. Cross point sub-array 2120 has a vertical physicaldimension Y=300 μm formed by 10,000 cells of periodicity 2F=30 nm.Spacing 2140 between horizontally placed cross point sub-arrays 2120 andspacing 2160 between vertically placed cross point sub-arrays 2120 arefor sub-array interconnections with underlying memory circuits (notshown). In this example, assuming spacing 2140 is 15% of the sub-array2120 horizontal X-dimension (45 nm), and spacing 2160 is 15% of thesub-array 2160 vertical Y-dimension (45 nm), then cross point sub-array2120 plus spacing will have a periodicity of X′=345 um and Y′=345 um inboth horizontal and vertical directions. In this example, there are 100cross point sub-arrays 2120 in each of the horizontal and verticaldirections. The resulting cross point memory array 2100 dimensions maybe calculated as 100×345 um, approximately 35 mm in both horizontalvertical directions. In this example, it is assumed that all memorycircuits may be placed and wired in regions below (and/or above) crosspoint memory array 2100, including interconnections with cross pointsub-arrays 2120. In this example, the combined areas of cross pointmemory array 2120 and input/output circuits (I/O circuits) andinterconnect terminals may be contained within chip dimensions of nomore than 50 mm×50 mm. For embedded memories, chip dimensions would beeven smaller.

With respect to FIG. 21, if minimum dimensions are scaled from F=15 nmto F=10 nm, then cell periodicity in sub-arrays 2120 are 20 nm. Assuming10,000 cells in the X and Y directions, then sub-array 2120 is squarewith dimensions of 200 nm. Allowing for sub-array-to-sub-array spacing2140 of 15% of the sub-array dimensions, then sub-array-to-sub-arrayperiodicity X′ and Y′ are 230 nm in both X and Y directions. For 100sub-arrays in both the X and Y directions, then corresponding memoryarray size is 23×23 mm. As described further above with respect to FIG.21, for a memory array formed with 100 sub-arrays in both X and Ydirections with F=15 nm, the memory array dimensions are 34.5×34.5 mm.Scaling from F=15 to F=10 nm results in a memory array size reduction of2.5 times.

At this point in the present disclosure, an estimate may be made of theapproximate maximum memory operating speed, that is, in the nanosecondor the microsecond range, for the 1 Tb cross point memory array 2100described further above with respect to FIG. 21. This estimated memoryspeed may be compared with chart 1800 (FIG. 18) to determine whichmemory applications are compatible with the maximum estimated operatingspeed when using sub-arrays formed with 1-R cells for example.

FIG. 22 illustrates an approximation of a structure for calculating thearray line capacitance of a cross point memory array with 1-Rnonvolatile cells, for example, arrays similar in cross section to crosspoint array 120 (FIG. 1B). Referring to FIG. 22, array wire 2220 onsubstrate 2210 corresponds to array wire 122 (FIG. 1B-3). Array wire2230 corresponds to array wire 126 in direct contact with porous switchnanotube block 136 by eliminating second electrical contact 138.Electric non-fringing field lines 2240 and fringing electrical fieldlines 2250 contribute to the array wire 2230 capacitance with respect toan underlying orthogonal grid of array wires (FIG. 1B-1), one of whichis array wire 2220. The direction of the electric field is shown as ifarray wire 2230 is at a positive voltage with respect to array wire2220. However, the voltage polarity may be reversed. As describedfurther above with respect to sub-arrays 2120 (FIG. 21), the array wire2230 width W_(AW)=15 nm, the length is 300 um, the insulator thicknesst_(INS)=20 nm, and the array wire thickness H_(AW)=200 nm. For such astructure, fringe electrical fields significantly increase thecapacitance of array wires beyond the non-fringing field capacitance byapproximately 5 times as estimated using equation 1 further below. Forrelatively high fringing fields, underlying orthogonal wire grids can beapproximated by a continuous plane.

The capacitance of individual NV CNT resistive block switches, such asNV CNT resistive block switch 104 illustrated in FIG. 1A, was measuredon a test site. NV CNT resistive block switch dimensions on the testsite were 250 nm×250 nm with a switch nanotube block, such as switchnanotube block 108, having a thickness of 50 nm and a porosity ofapproximately 90%. The capacitance was so small that it could only bedetermined to be substantially less than 1 fF. For a parallel-platecapacitor with plate dimensions of 15 nm×15 nm, a plate-to-platecapacitance separation of 20 nm, and top and bottom electrodethicknesses of 200 nm, and even assuming a dielectric with a relativeconstant as high as ∈_(R)=16 and a fringing field multiplier of 5 times,the parallel plate capacitance is less than 10×10⁻¹⁸ F; that is, acapacitance of <10 aF. A porous switch nanotube block may increase thecapacitance because of CNT-to-CNT capacitance and CNT-to-electrodecapacitance. However, with ∈_(R)=1 between the CNTs in the CNT fabricand the CNT-to-electrodes, the effect is likely to be small as indicatedby test site results.

The array wire delay is estimated as described further below. In thisexample, array wires 2125 and 2130 (FIG. 21) are assumed to have thesame length of 300 μm as described further above. Cross section 2200 isan approximation of a cross section through array wire 2125 or 2130, inwhich array wire cross section 2230 corresponds to an array wire 2125 or2130 cross section. Array wire 2220 is one of multiple parallel arraywires that are orthogonal to array wire 2230, and which are approximatedby a conductive plane as described further above with respect to FIG.22.

Equation 1 may be used to calculate array wire capacitance per unitlength C_(AW)/l, including fringing fields, as described in thereference H. B. Bakoglu, “Circuits, Interconnections and Packaging forVLSI”, Addison-Wesley Publishing Company, 1990, pages 137-139.C _(AW) /l=∈ ₀∈_(R) {W _(AW) /t _(INS) −H _(AW)/2t _(INS)+2π/(ln [1+(2t_(INS) /H _(AW))·(1+(1+H _(AW) /t _(INS))^(0.5))])}  [EQ 1]where:

∈₀=8.854×10⁻¹² F/m;

∈_(R)=4;

W_(AW)=15 nm;

H_(AW)=200 nm; and

t_(INS)=20 nm

Substituting in equation 1:C _(AW) /l=8.854×10⁻¹²×4{15/20−200/40+2π/(ln[1+(40/200)·(1+(1+200/20)^(0.5))])}results in an array wire capacitance per unit length of:C _(AW) /l=207×10⁻¹² F/m  [EQ 2]as shown in equation 2. For an array wire of length l=300 um,C _(AW)=207×10⁻¹² F/m×300×10⁻⁶ m/um

Array wire capacitance C_(AW) for 300 um array lines, such as arraylines 2125 or 2130 illustrated in FIG. 21, has an estimated capacitancevalue of:C _(AW)=62×10⁻¹⁵ F; or C _(AW)=62 fF  [EQ 3]

As described further above with respect to FIG. 3B, the minimum onresistance R_(ON)=100 MΩ for a NV CNT resistive block switch in a 100 Mbsub-array, such as sub-array 2120 (FIG. 21). The maximum performancerange (microsecond or nanosecond) may be estimated using an RC delaytime constant in which the resistive state of a NV CNT resistive blockswitch with R_(ON)=100 M, connected to an array line such as array line2125 or 2130, is read-out. Multiplying the R_(ON) value and the arraywire capacitance C_(AW) results in an RC time constant of:R _(ON) C _(AW)=100×10⁶×62×10⁻¹⁵=6.2 us  [EQ 4]6.2 microseconds (equation 4). The rise (and fall time) of waveforms onarray wires may be approximated as 2.2 R_(ON)C_(AW) as described in thereference: H. B. Bakoglu “Circuits, Interconnections and Packaging forVLSI”, Addison-Wesley Publishing Company, 1990, pages 239-241. In thisexample, the rise time t_(R) may be estimated as shown in equation 5.t _(R)=2.2 R _(ON) C _(AW) ; t _(R)=2.2×6.2; t _(R)=13.6 us  [EQ 5]

The equation 5 rise time t_(R) estimate indicates that a 1 Terabitnonvolatile memory, such as described further above with respect to FIG.21, and formed with 10,000 100-megabit sub-arrays of interconnected 1-Rcells with NV CNT resistive block switches of a minimum resistanceR_(ON)=100 MΩ, operates in the microsecond performance range. The Arraywire C_(AW) capacitance of 62 fF (equation 3) is a relatively low arrayline capacitance value. However, the NV CNT resistive block switchminimum resistance R_(ON)=100 MΩ is relatively high in order to enable asub-array size of 100 megabits as described further above with respectto FIG. 3B, which results in a maximum estimated memory performance(speed of operation) in the microsecond range, limited by the multiplesub-array 2120 performance used in cross point memory array 2100 (FIG.21) and as calculated further above based on equations 1-5.

A 1 terabit nonvolatile memory chip in the microsecond range has manyapplications. Such chips may be used to form a solid state drive (SSD)1840 shown in chart 1800 illustrated in FIG. 18. Microsecond operationmay also be used in many microcontroller applications, but not inmicrocontroller applications requiring nanosecond performance such asNRAM 1820. And there are other applications for microsecond performancenonvolatile memory chips not shown in chart 1800.

As illustrated further above with respect to equations 1-5, fornanosecond operation, the minimum resistance R_(ON) must besubstantially reduced below 100 MΩ since the array wire capacitance isalready relatively low. NRAMs formed with memory arrays using 1-T, 1-Rresistive memory cells 100 with a MOSFET select devices enable NV CNTresistive block switches 104 (FIG. 1A) with ON resistance values of 100kΩ as described further above with respect to FIG. 19, and have 1000times smaller low resistance state values than the 1-R cells describedfurther above but are not sufficiently scalable. However, 100 kΩ minimumvalues would limit 1-R cells to approximately 100 bits per sub-arraybased on cross point array requirements 320 and curve 325 shown in FIG.3B, and therefore compatible only with small memory sizes of perhaps afew thousand bits.

Achieving nanosecond performance terabit nonvolatile memory chipsrequires sub-arrays of 100 Mb or larger with ON resistance values of 100kΩ, while eliminating or minimizing current sneak paths 235 illustratedin FIG. 2A, and compatible with 4F² cell dimensions of 30 nm×30 nm atthe 15 nm technology node. What is needed is the addition of arelatively high selectivity in NV CNT resistive block switches (RSswitches) to achieve high selectivity 1-RS cells, with the samefootprint as 1-R cells. However, the switch nanotube block thicknesscannot increase significantly above approximately 20 nm at the 15 nmtechnology node as discussed above with respect to FIG. 22 for reasonsof image resolution, and also so as not to increase array wire fringingelectric fields 2250 (FIG. 22) that may couple to adjacent array lines.

NV CNT resistive block switches 104 (FIG. 1A) described further above inFIG. 19 were fabricated with mostly MWCNTs. However, NV CNT resistiveblock switches 104 have recently been fabricated with CNT fabrics formedwith metallic and semiconducting SWCNTs having approximately the sameelectrical characteristics as described in FIG. 19. The smaller diameterof SWCNTs compared with MWCNTs results in a lower switch CNT blockthickness and may be used to facilitate increasing the selectivity of NVCNT resistive block switches without increasing the overall thickness.

Dense high selectivity 1-RS cells require that a high selectivity diode,that is, having relatively low forward resistance and relatively highreverse leakage current, be integrated with a NV CNT resistive blockswitch optimized for nonvolatile storage, at approximately 4F² cell sizeat the 15 nm technology node, for example. Such dense 1-RS cells may beformed by leveraging the multi-layer NV CNT resistive block switchfabrication methods. For example, semiconducting CNT fabrics may bedeveloped with low defect levels that are compatible with semiconductorfabricator processes and tools, and compatible with multi-wall mostlymetallic CNT fabrics, and single-wall mixed metallic and semiconductingCNTs, presently used to form NV CNT resistive block switches in NRAMcells. In this way, an integrated select diode (Schottky or p/n forexample) and a CNT block may be optimized to achieve a 1-RS cross pointcell compatible with terabit memory chips operating in the nanosecondrange. A semiconducting CNT fabric may be formed with available or to beavailable 90-99.999% single wall CNTs using methods similar to thosepresently used to make fabrics illustrated and described further abovewith respect to SEM image 1200 illustrated in FIG. 12A and SEM image1250 illustrated in FIG. 12B.

FIG. 23A illustrates cross point array 2300 formed with interconnected1-RS cells 2350 illustrated in FIG. 23B. Each 1-RS cell 2350 includesintegrated NV resistive switch 2360 and integrated diode 2370, with thecathode terminal connected to one terminal of NV resistive switch 2360.Integrated NV resistive switch 2360 is connected to an array wire atnode 1 and integrated diode 2370 is connected to another array wire atnode 2. Integrated diode 2370 has a sufficiently large write forwardcurrent to switch integrated NV resistive switch 2360 between multiplelow and high resistance states, and sufficiently low reverse leakagecurrent to eliminate, or minimize, parasitic currents from adjacentarray cells. For example, 1-RS cell 2350 may operate with a forwardcurrent to reverse current ratio of 10/1 to 100/1. Integrated NVresistive switch 2360 may be formed as switch nanotube block fabriclayers of various combinations of semiconducting and metallic SWNTs andMWNTs carbon nanotubes, switch graphitic layers, or switch buckyballlayers as described further above with respect to FIGS. 4, 5, 6, and 7.Integrated diode 2370 may be formed as diode nanotube fabric layers,diode graphitic layers, or diode buckyball layers. Integrated diode 2370may also be formed as diode nanotube fabric layers in contact with afirst or second conductor (or semiconductor or carbon conductor) layer,diode graphitic layers in contact with a first or second conductor (orsemiconductor or carbon conductor) layer, or diode buckyball layers incontact with a first or second conductor (or semiconductor or carbonconductor) layer. Integrated diodes may introduce a voltage drop of0.15-0.6 volts as a function of diode type (Schottky or PN diode forexample) and material choices. Voltage V shown in FIG. 23A may beincreased to compensate for integrated diode voltage drops as needed.Schottky diodes typically have forward voltage drops in the 0.15-0.45 Vrange. PN diodes have forward voltage drops of 0.3 for Ge and 0.6 V forSi. Diodes formed between conductors (or semiconductors) and carbonnanotubes have forward voltage drops in these ranges, and depend onbarrier heights between the conductor and the carbon nanotubes.

While FIG. 23A illustrates cross point array 2300 formed withinterconnected 1-RS cells 2350 illustrated in FIG. 23B, cross pointarray 2300 may also be formed with interconnected 1-RS cells 2380illustrated in FIG. 23C. Each 1-RS cell 2380 includes integrated NVresistive switch 2385 and integrated diode 2390, with the anode terminalof integrated diode 2390 connected to one terminal of NV resistiveswitch 2385.

Cross point array 2300 illustrated in FIG. 23A is formed withinterconnected 1-RS cells 2350 illustrated in FIG. 23B. Parallelhorizontal array wires 2302, 2304, and 2306 are approximately orthogonalto parallel vertical array wires 2312, 1214, and 1216. 1-RS cell C00 isformed by connecting array wire 2302 to node 1 and connecting array wire2312 to node 2; 1-RS cell C01 is formed by connecting array wire 2302 tonode 1 and connecting array wire 2314 to node 2; 1-RS cell C02 is formedby connecting array wire 2302 to node 1 and connecting array wire 2316to node 2; 1-RS cell C10 is formed by connecting array wire 2304 to node1 and connecting array wire 2312 to node 2; 1-RS cell C11 is formed byconnecting array wire 2304 to node 1 and connecting array wire 2314 tonode 2; 1-RS cell C12 is formed by connecting array wire 2304 to node 1and connecting array wire 2316 to node 2; 1-RS cell C20 is formed byconnecting array wire 2306 to node 1 and connecting array wire 2312 tonode 2; 1-RS cell C21 is formed by connecting array wire 2306 to node 1and connecting array wire 2314 to node 2; 1-RS cell C22 is formed byconnecting array wire 2306 to node 1 and connecting array wire 2316 tonode 2.

In operation, 1-RS cell C11 is selected by applying a voltage V tovertical array line 2314 and a voltage V=0 voltage to horizontal arrayline 2304 resulting in current 2330 if 1-RS cell C11 is in a lowresistance state. If cell C11 is in a high resistance state, thencurrent 2330 is a low leakage current, which is not detected by a senseamplifier. However, 1-RS cell C11 may contain multiple resistancestates. For example, four resistance states may store two bits ofinformation in 1-RS cell C11; eight resistance states may store threebits of information in 1-RS cell C11; and so on as described withrespect to U.S. Pat. No. 8,102,018. Unselected 1-RS cells C00, C20, C02,and C22 are biased across terminals 1 and 2 such that integrated diodes2370 are biased in the reverse direction (back biased) and do notconduct or conduct a negligibly small leakage current. Unselected 1-RScells C01, C10, C12, and C21 have equal voltages applied acrossterminals 1 and 2 and no parasitic currents flow.

At this point in the present disclosure, an estimate may be made of theapproximate maximum memory operating speed, that is, in the nanosecondor the microsecond range, for 1 Tb cross point memory array 2100described further above with respect to FIG. 21 with sub-arrays 2120corresponding to cross point array 2300 illustrated in FIG. 23, formedwith 1-RS cells. This estimated memory speed may be compared with chart1800 (FIG. 18) to determine which memory applications are compatiblewith maximum estimated operating speeds when using sub-arrays formedwith 1-RS cells. The estimated memory speed for sub-arrays formed with1-RS cells may be calculated using the same methods and equationsdescribed further above with respect to equations 1-5.

In this example, array wires 2125 and 2130 (FIG. 21) formed with crosspoint array 2300 (FIG. 23A) have the same length of 300 um as describedfurther above, with cross section 2200 approximating a cross sectionthrough array wire 2125 or 2130, in which array wire cross section 2230corresponds to an array wire 2125 or 2130 cross section. Array wire 2220is one of multiple parallel array wires that are orthogonal to arraywire 2230, and which are approximated by a conductive plane as describedfurther above with respect to FIG. 22. Accordingly, the array wirecapacitance calculated using equations 1-3 further above may be used forarray wires 2125 and 2130 when formed with cross point array 2300 (FIG.23A), that is, 62 fF. The array wire RC time constant may be calculatedusing equation 4, and the rise (or fall) time may be calculated usingequation 5 for low resistance state R_(ON) values corresponding to 1-RScells 2350 illustrated in FIG. 23B.

Estimated sub-array performances may be calculated as illustratedfurther below for sub-arrays 2120 formed with cross point arrays 2300.The 1-RS cell 2350 low resistance state R_(ON)=100 kΩ and the array wirecapacitance C_(AW)=62 fF as calculated above for each sub-array example.Time constant and rise time examples are calculated in Eq. 6 and 7 asfollows:

For sub-arrays with 10,000 1-RS cells per array wire 2125 and 2130:C _(AW)=62×10⁻¹⁵ F; or C _(AW)=62 fF, from equation 3;R _(ON) C _(AW)=10⁵×62×10⁻¹⁵=6.2 ns  [Eq. 6]t _(R)=2.2 R _(ON) C _(AW) ; t _(R)=2.2×6.2; t _(R)=13.6 ns  [Eq. 7]and the cross point memory arrays with 1-RS cells are approximately 1000times faster than cross point memory arrays with 1-R cells for the samearray sizes.

For sub-arrays with 20,000 1-RS cells per array wire 2125 and 2130:

In this example, there are two times the number of cells per sub-arraywire, the array wire length increases to 600 um, and array wirecapacitance increases by 2 times. The number of sub-arrays needed toform a 1 Tb memory array is reduced from 10,000 to 2,500 sub-arrays.However, 10,000 sub-arrays may be used instead, resulting in 4 Tb memorychip.C _(AW)=2×62×10⁻¹⁵ F; or C _(AW)=124 fF, from equation 3;  [Eq. 8]R _(ON) C _(AW)=10⁵×124×10⁻¹⁵=12.4 ns  [Eq. 9]t _(R)=2.2 R _(ON) C _(AW) ; t _(R)=2.2×12.4; t _(R)=27.3 ns  [Eq. 10]

Equation 7 and 10 rise times t_(R) estimates indicates that a 1 Terabitand 4 Terabit nonvolatile memories, such as described further above withrespect to FIGS. 21, 22, 23, and formed with 10,000 100-megabitsub-arrays and 400-megabit arrays, respectively, of interconnected 1-RScells with NV CNT resistive block switches of a minimum resistanceR_(ON)=100 kΩ, operates in the nanosecond performance range. The arraywire C_(AW) capacitance values of 62 fF (equation 3) and 124 fF(equation 8) are relatively low array line capacitance values. The NVCNT resistive block switch minimum resistance R_(ON)=100 MΩ isrelatively low when using 1-RS cells in sub-array sizes of 100 megabitsas described further above with respect to FIGS. 21, 22, and 23. Thecombination of relatively low array line capacitance and relatively lowminimum resistance R_(ON) values results in a maximum estimated memoryperformance (speed of operation) in the nanosecond range as shown byequations 7 and 10.

A 1 terabit nonvolatile memory chip in the nanosecond range has manyapplications. These terabit nanosecond memory chips meet the nonvolatilerandom access nanosecond speed memory objectives described further abovewith respect to FIG. 18, which includes the following: NRAM 1810 forcell phones, and numerous other applications (not shown); NV RAM 1820 asembedded memories in microcontroller chips, and numerous otherapplications (not shown); SCM memory 1830 and solid state drive 1840 forcomputer applications, and numerous other applications (not shown).

Structures and Methods of Fabrication of Cross Point Memory Arrays

FIGS. 8C, 8D, and 8E show the patterning of adjacent cross point arraycells into stacks by etching multiple layers, followed by sidewallpassivation and dielectric fill between the stacks, such as sidewallpassivation 850 and dielectric fill 852 illustrated in FIG. 8E. Suchmethods have been successfully used with respect to NRAM memories usingNV resistive memory cell 100 illustrated in FIG. 1A. However, for crosspoint arrays scaled to minimum dimensions such as F=15 nm and smaller,it may be desirable to use fabrication methods that do not requiresidewall passivation of switch nanotube fabric layers, such as switchnanotube fabric layer 824 with sidewall passivation 850 illustrated inFIG. 8E, in order to prevent possible penetration of the passivationlayer into switch nanotube fabric layers from the sides as that couldalter the electrical switching characteristics.

One method described in U.S. Patent Pub. No. US 2006/0276056 teachesconverting portions of a carbon nanotube fabric from a conducting to anonconducting fabric; such patterning is done by converting portions ofthe CNT fabric to an electrically nonconducting state while otherportions are left electrically conducting. FIGS. 24A-24C illustratestructures corresponding to fabrication methods to form CNT fabric 2445with conducting regions 2432 and nonconducting regions 2434 shown bystructure 2440 illustrated in FIG. 24C. Nonconducting CNT fabric regionsmay be used as an insulating layer preventing undesired current flowbetween adjacent cells (adjacent bit disturb) in a cross point array forexample as an alternative to trench isolation described further above.

Structure 2400 illustrated in FIG. 24A shows conducting CNT fabric 2406formed with conducting and/or semiconducting carbon nanotubes, on anunderlying layer 2404, which is on substrate 2402. Substrate 2402 may beformed of a semiconductor with CMOS circuits that may be used to operatea cross point array. Underlying layer 2404 may be an insulator thatincludes filled via holes to contact underlying CMOS circuits, firstelectrical terminals, arrays wires, and diodes used to form cross pointinterconnected cross point cells overlying substrate 2402, that aresimilar to those described further above with respect to FIGS. 1B-1,1B-2, and 1B-3. A patterned masking layer 2412 may be formed using knownmethods of fabrication. Patterned masking layer 2412 may be formed as asacrificial layer using a resist. Alternatively, patterned masking layer2412 may be a second conductive terminal, such as second conductiveterminal 138 illustrated in FIG. 1B-2, which may be used as a maskinglayer and is not etched away.

Conductive CNT fabric 2406 illustrated in FIG. 24A has exposed regions2422. Structure 2400 is exposed to a Reactive Ion Etch (RIE) plasma suchas CF₄, CHF₃, etc. in order to change the electrical properties of theexposed regions 2422 of conductive CNT fabric 2406. Unprotected portions2422 of the CNT fabric will be fully converted to a nonconductive CNTfabric 2434, thus forming intermediate structure 2430 illustrated inFIG. 24B. The masking pattern protects the underlying CNT fabric fromthe plasma, preventing conversion to a non-conducting CNT fabric. AfterRIE plasma exposure, the pattern mask may be removed, as illustrated instructure 2440 illustrated in FIG. 24C. CNT fabric 2445 is a CNT fabricwith conducting CNT fabric regions 2432 and nonconducting CNT fabricregions 2434 as illustrated in FIG. 24C. If the masking layer 2412 isalso a second conductive terminal, then it remains on the surface of CNTfabric 2445 over conducting CNT fabric regions 2432. Ion implantation,such as illustrated in FIGS. 4C-4E, and other known methods, may also beused instead of a RIE plasma. Examples of ion implantation and othermethods are illustrated in U.S. patent application Ser. No. 12/066,053and U.S. patent application Ser. No. 12/874,501.

Field Emission Scanning Electron Microscope (FESEM) 2500 illustrated inFIG. 25 shows a CNT fabric deposited on a substrate with bond pads, suchas bond pads 2510 and 2515, after non-protected regions of the CNTfabric have been converted to nonconductive CNT fabric 2534 to providecell-to-cell isolation. The conducting. CNT fabric 2532 remainsconducting in the protected region.

A layer of carbon nanotubes from several nanometers up to a micron thickmay be applied to the substrate either by spray coating, spin coating,dip coating, etc. Then, a mask pattern is fabricated on top of the CNTfabric by spinning, exposing, and developing photoresist. The carbonnanotubes are then exposed to a typical reactive ion etching (RIE) gassuch as CF₄, CHF₃, etc. The RIE gas reacts with the unmasked carbonnanotubes to convert the conducting nanotubes into nonconductingnanotubes. Care can be taken to minimize morphological damage to the CNTfabric while changing the electrical properties from conducting tononconducting. Single and multilayer depositions of CNT layers may beused. As an example, a carbon nanotube fabric is sprayed onto asubstrate to produce a low Ohm resistance fabric (<50Ω per square).After depositing the CNT fabric, the substrate is loaded into an RIEchamber containing CF₄ gas is at a pressure of 30 mTorr at 30 Watts for30 seconds. Unprotected portions of the CNT fabric were fully convertedto an insulating fabric, while the mask prevented the underlying portionfrom being converted to a non-conducting CNT fabric. After RIE plasmaexposure, the patterned mask was removed, leaving a patterned conductingCNT fabric 2532 within the nonconducting CNT fabric 2534 as illustratedin FIG. 25. Processing conditions are not limited to these parameters.

FESEM 2600 illustrated in FIG. 26 shows a magnified view of adjacentnonconductive CNT fabric 2534 and conductive CNT fabric 2532 regionsfrom FIG. 25.

At this point in the present disclosure, structures and methodsdescribed further above with respect to FIGS. 24, 25, and 26 may be usedto convert conductive CNT fabrics to nonconductive CNT fabrics forcell-to-cell isolation, and may be applied to cross point array 120illustrated in FIGS. 1B-1, 1B-2, and 1B-3 as an alternative to thestructures and methods using sidewall passivation and dielectric fill852 illustrated in FIG. 8E for cell-to-cell isolation. In manyapplications, nonconductive CNT fabric 2434 used for cell-to-cellisolation may be converted to high-resistance CNT fabric regions insteadof nonconductive CNT fabric regions, in which the high-resistance issufficiently high to prevent significant cell-to-cell leakage.

FIG. 27A illustrates plan view 2700 of a cross point array formed with acontinuous CNT fabric plane 2706 deposited on top of the planarizedsurface of underlying layer 2704, which corresponds to underlying layer2404 illustrated in FIG. 24A. Cross section 2750, illustrated in FIG.27B, is a representation of cross section A-A′ in FIG. 27A In thisexample, underlying layer 2704 includes array wires 2703, which alsoform first conductor terminals 2703, embedded in a dielectric 2701 asillustrated in FIG. 27B. First conductor terminal 2703 corresponds tofirst conductor terminal 134 shown in FIG. 1B-2. CNT fabric plane 2706replaces discrete NV CNT resistive block switches 130-1, 130-2, 130-3,and 130-4 illustrated in FIG. 1B-1. In this example, second conductorterminals 2738 are formed on the surface of CNT fabric plane 2738 atlocations corresponding cross point array switches and corresponds tosecond conductive terminal 138 illustrated in FIGS. 1B-2. In thisexample, second conductive terminals 2738 are also used as a maskinglayer.

FIG. 28A illustrates plan view 2800 of the cross point array illustratedin plan view 2700 and corresponding cross section 2850 shown in FIG. 28Bafter exposed areas of CNT fabric plane 2706 have been exposed to CF₄gas, ion implantation, or other methods described further above to formhigh-resistance or nonconductive CNT fabric 2834 regions. Non-exposedareas of CNT fabric plane 2706, located under second conductor terminals2738, remain conducting CNT fabric regions 2832 as illustrated in FIG.28B. Nonconductive CNT fabric 2834 regions isolate conductive CNT fabricregions 2832 that form NV CNT resistive block switches corresponding toNV CNT resistive block switches 130-1, 130-2, 130-3, and 130-4illustrated in FIG. 1B-1.

FIG. 29 illustrates cross section 2900 in which an insulation layer hasbeen deposited and planarized on the structures illustrated in FIGS. 28Aand 28B using known methods to form insulator 2940. Insulator 2940 maybe formed using SiO₂, SiN, Al₂O₃, and other insulator materials.Insulator material 2940 is unlikely to significantly penetrate theconductive CNT regions 2832 between second conductor terminal 2738 andfirst conductor terminal 2703.

FIG. 30 illustrates cross section 3000 after the deposition andpatterning of array top wire 3050, corresponding to array top wire 126illustrated in FIG. 1B-2. As this point in the process, cross pointarray cells have been formed with high-resistance or nonconductive CNTfabric regions isolating adjacent cells, instead of sidewall passivationand dielectric fill.

While the example illustrated in FIGS. 24-30 have been illustrated withCNT fabrics, the same principles may be applied to graphitic fabricsused to form switch graphitic blocks 168 (FIG. 1D) and buckyball fabricsused to form switch buckyball blocks 188 (FIG. 1E). For example, FIG. 31illustrates cross section 3100 corresponding to cross section 3000illustrated in FIG. 30, except that conductive CNT fabrics andhigh-resistance or nonconductive CNT fabric regions have been replacedwith conductive and nonconductive graphitic layer regions. For example,conductive graphitic layers 3132 form the nonvolatile storage switchesin cross point array cells and high-resistance or nonconductivegraphitic layers 3134 are used for isolation between cross point arraycells. In another example, FIG. 32 illustrates cross section 3200corresponding to cross section 3000 illustrated in FIG. 30, except thatconductive CNT fabric and nonconductive CNT fabric regions have beenreplaced with conductive and high-resistance or nonconductive buckyballlayer regions. For example, conductive buckyball layers 3232 form thenonvolatile storage switches in cross point array cells andhigh-resistance or nonconductive buckyball layers 3234 are used forisolation between cross point array cells.

Methods of Fabrication and Structures of Cross Point Memory ArraysFormed with Continuous CNT Fabrics and Intersecting Array Lines ofMinimum Width F

Scaling cross point arrays to sub-15 nm minimum dimensions and sub-10 nmminimum dimensions, requires process methods and structures that addressvarious limitations to scaling. Of the various dimensional scalinglimitations, there are several limitations with respect to forming CNTswitching regions described further below with respect to methods 3300and structures illustrated in FIGS. 34A-39. While these are not the onlylimitations, they are among the most difficult to overcome and arelisted as problems 1, 2, and 3 further below. These problems aredescribed with respect to cross point array 120 illustrated in FIGS.1B-1, 1B-2, and 1B-3. F is used to indicate a minimum dimension.

1) Forming Multiple F×F Structures: Cross point array 120 shows a topelectrode, referred to as second electrical contact 138. It hasdimensions F×F and is also used as an etch mask to define switchnanotube block 136 dimensions of F×F. Minimum dimension shapes of F×F,as drawn, typically result in circular etch mask shapes. Ideally, thesewould all have a diameter F, or at least the same diameter even ifsmaller than F for example. However, the various circular mask shapedimensions may vary over the chip surface, and in some cases may bemissing altogether at some locations.

2) Forming Switch Nanotube Block Structures: As illustrated in crosspoint array 120 FIGS. 1B-2 and 1B-3, second electrical contact 138 isalso used as an etch mask to etch a CNT layer and form switch nanotubeblock 136 of minimum dimensions F, ideally having the same cross sectionas second electrical contact 138. However, even with the use ofdirectional etch some undercutting and non-uniformity may occur inswitch nanotube block 136. A combination of the second electricalcontact 138, switch nanotube block 136, and the first electrical contact134 form NV CNT block switch 130-1.

3) Insulating NV CNT Block Switches: As illustrated in FIGS. 1B-1, 1B-2and 1B-3, insulator 132 is used between NV CNT block switches 130-1,130-2, 130-3, and 130-4 in two-by-two cross point array 120. These NVCNT block switches include a switch nanotube block of patterned CNTfabric which is porous. Insulator 132 may penetrate the porous sidewallsof the NV CNT block switches and change the electrical switchingproperties.

Approaches to solving problems 2 and 3 are described and illustratedwith respect FIGS. 24A-30 as described further above. However, thesesolutions require formation of a top contact of minimum dimensions F×F,a scaling limitation as described above with respect to problem 1. Anapproach to solving problem 1 is described below with respect to methods(of fabrication) 3300 illustrated in FIGS. 33A, 33B, and 33C andstructures illustrated in FIGS. 34A-39. This approach is based on usingoverlapping array wires of F×l, dimensions, where l is much greater thanminimum dimension F, and where the regions of array wire overlap aredimensionally F×F as illustrated further below. A contact layer remainson the surface of the CNT fabric layer to protect CNTs from the variousprocess steps until just prior to passivation. Ion implantation throughthe contact layer is used to form high-R CNT fabric isolation regionsbetween CNT fabric conducting regions, while preserving F×F CNTswitching regions below overlapping array wire regions. Then, at the endof the process flow, exposed regions of the contact layer are removed(etched) using top array wires as a masking layer. Methods 3300illustrate methods of fabrication and structures that may be used tofabricate cross point memory array 2100 illustrated schematically inFIG. 21.

Methods (of fabrication) 3300 flow chart illustrated in FIGS. 33A, 33B,and 33C describe methods (processes) of forming structures illustratedin FIGS. 34A-39. Variations to methods of fabrication 3300 such as theaddition or omission of steps and varying the order of steps are stillwithin the scope described below with respect to FIGS. 33A, 33B, and 33Cand FIGS. 34A-39.

Methods 3300 and structures illustrated in FIGS. 34A-39 form cross pointmemory arrays, or sub-arrays, which correspond to cross point memoryarray 2100 and sub-arrays 2120, and cross point memory array 2300,illustrated schematically in FIGS. 21 and 23, respectively. By way ofexample, bottom array wire 3404 illustrated in FIG. 34A, may have aminimum width F and X-direction length l_(X), and corresponds toX-direction array wire 2125. By way of example, top array wire 3430illustrated in FIG. 34C, may have a minimum width F and Y-directionlength l_(Y), and corresponds to Y-direction array wire 2130. Frepresents the minimum dimension at a technology node, 2F represents theminimum periodicity along an array wire, and array wire lengths l_(X)and l_(Y) are determined by the number of bits along each array wire asdescribed further above with respect to FIG. 21. Array wires lengthsl_(X) and l_(Y) may be of the same length l, or different lengths.

Methods 3300 assumes that substrate 3402 illustrated in FIG. 34Aincludes many of the components of n and p-type field effect devices(MOSFETs) with drain, source, and gate nodes, interconnections to formcircuits (typically CMOS circuits) in support of the memory function tobe fabricated on the surface of substrate 3402. And, also thatconnections between memory arrays and sub-arrays formed on the surfaceof substrate 3402 and the underlying circuits are present withinsubstrate 3402.

Methods 3310 deposit a conductor layer on the surface of substrate 3402illustrated in plan view 3400 shown in FIG. 34A using known industrymethods, or methods described further below in the case of nanotubefabrics for example. Thicknesses may range from 5 nm to 500 nm forexample. The term conductor may include metals, metal alloys,semiconductors, silicides, conductive oxides, various allotropes ofcarbon, and other materials. The following are examples of conductors,conductive alloys, and conductive oxides: Al, Al(Cu), Ag, Au, Bi, Ca,Co, CoSi_(x), Cr, Cu, Fe, In, Ir, Mg, Mo, MoSi₂, Na, Ni, NiSi_(x), Os,Pb, PbSn, PbIn, Pd, Pd2Si, Pt, PtSi_(x), Rh, RhSi, Ru, RuO, Sb, Sn, Ta,TaN, Ti, TiN, TiAu, TiCu, TiPd, TiSi_(x), TiW, W, WSi₂, Zn, ZrSi₂, andothers for example.

The following are examples of semiconductors that may be used asconductors: Si (doped and undoped), Ge, SiC, GaP, GaAs, GaSb, InP, InAs,InSb, ZnS, ZnSe, CdS, CdSe, CdTe, GaN, and other examples.

Various allotropes of carbon may also be used as conductors such as:amorphous carbon (aC), carbon nanotubes such as nanotube fabrics,graphite, buckyballs, and other examples.

In addition to the materials described further above such conductors,semiconductors, conductive oxides, and allotropes of carbon, nanowiresformed of various conductor, semiconductor, and conductive oxidematerials, such as those described further above, may also be used aswell.

Optionally, methods 3310 may deposit another conductive layer, which maybe referred to as a second conductive layer. The first conductive layerdeposited may be optimized for array wiring and the second conductivelayer may be used to enhance contact properties between the firstconductive layer and the CNT fabric layer. The second conductive layermay be formed with any of the materials described further above withrespect to methods 3310. FIG. 34A shows a bottom array wires as formedfrom one conductor layer. However, optionally, two conductors may beused as described.

Next, methods 3310 deposit a resist layer, expose and develop theresist, then etch to pattern array wires on the surface of substrate3402 using known industry methods forming array wires 3404 asillustrated by plan view 3400 in FIG. 34A. Array wire 3404 width may bescaled over a large range: on the order of 250 nm to on the order of 10nm. Methods 3300 may be used to form array wire 3404 widths of less than10 nm.

Next, methods 3310 deposit an insulating layer using known industrymethods to a thickness of 5 to 500 nm for example. Examples ofinsulators are SiO₂, SiN, Al₂O₃, TEOS, polyimide, HfO₂, TaO₅,combinations of these insulator materials and other insulator materials.

Then, methods 3310 planarize the insulating layer to the top surface ofarray wires 3404 using known industry methods, forming insulator 3406,as illustrated by cross section 3410 illustrated in FIG. 34B along the Ydirection and corresponds to cross section CC′ shown in FIG. 34A.

Next, methods 3320 deposit a CNT layer, or several CNT layers, asillustrated in plan view 3420 and cross sections 3420-1, 3420-2, and3420-3 in the X-direction illustrated in FIGS. 34C, 34D-1, 34D-2, and34D-3, respectively, to form a porous unordered carbon nanotube (CNT)fabric layer, such as CNT fabric layer 3422, or 3424, or 3426 of mattedcarbon nanotubes as shown in FIGS. 34D-1, 34-2, and 34D-3, respectively.Cross sections 3420-1, 3420-2, and 3420-3 correspond to cross sectionDD′ shown in FIG. 34C. CNT fabric layer 3422 illustrated in FIG. 34D-1may be used to form 1-R type nonvolatile resistive change memory cells(or elements) as described further above with respect to FIG. 1C. CNTfabric layer 3426 may be used to form 1-RS type nonvolatile resistivechange memory cells (or elements) as described further above withrespect to FIG. 4B, in which switch nanotube fabric layer 3426A isintegrated with diode nanotube fabric layer 3426B for high cellselectivity as illustrated in FIG. 34D-3. Alternatively, the integrateddiode nanotube fabric layer may be placed above the switch nanotubefabric layer such as illustrated by CNT fabric layer 3424 in which diodenanotube fabric layer 3424B is placed above switch nanotube layer 3424Aas illustrated in FIG. 34D-2. For the structures described furtherbelow, CNT fabric layer 3426 illustrated in FIG. 34D-3 will be used.While diode nanotube fabric layers have been illustrated at the top orbottom of CNT fabric layers, such diode fabric layers may be includedanywhere in the CNT fabric layer. Multiple diode fabric layers may beincluded as well (not shown).

An unordered nanotube fabric layer deposited on a substrate element isshown by the scanning electron microscope (SEM) image 1200 illustratedin FIG. 12A. This may be done with spin-on technique or otherappropriate technique as described in U.S. Pat. Nos. 6,643,165,6,574,130, 6,919,592, 6,911,682, 6,784,028, 6,706,402, 6,835,591,7,560,136, 7,566,478, 7,335,395, 7,259,410 and 6,924,538, and U.S.Patent Pub. No. 2009/0087630, the contents of which are herebyincorporated by reference in their entireties (hereinafter andhereinbefore, the “incorporated patent references”). Under preferredembodiments, the carbon nanotube layer may have a thickness ofapproximately 0.5-500 nm for example. The CNT layer may be formed ofmultiwalled nanotubes, single wall nanotubes, metallic nanotubes,semiconductor nanotubes, and various combinations of all nanotube types,doped and functionalized as described in more detail in U.S. patentapplication Ser. No. 12/356,447 and U.S. patent application Ser. No.12/874,501, herein incorporated by reference in their entirety.

Alternatively, methods 3320 may, after the deposition of one or more CNTlayers such as described further above, use mechanical or other methods,to approximately align some or most of the nanotubes in a preferreddirection to form an ordered nanotube fabric layer, or several orderednanotube layers, as described in U.S. Patent App. No. 61/319,034.Ordered nanotube fabrics may be ordered throughout the nanotube fabricthickness. However, ordered nanotube fabrics may be present for only aportion of the nanotube fabric thickness, while the rest of the nanotubefabric remains an unordered fabric. Ordered and unordered nanotubefabrics may be present in multiple layers that form CNT fabric layers3422, 3424, and 3426. FIG. 12B illustrates a scanning electronmicroscope (SEM) image 1250 of an ordered nanotube fabric.

Next, methods 3330 deposit contact layer 3428 over CNT fabric layer3422, or 3424, or 3426, as illustrated in FIGS. 34D-1, 34D-2, and 34D-3,respectively, in a thickness range of 1 nm to 100 nm as needed usingknown industry methods. Contact layer 3428 may be formed usingconductive material, semiconductive material, or various allotropes ofcarbon, and other materials, as discussed further above with respect tomethods 3310. Contact layer 3428 is used to enhance resistive changememory cell (or element) switching characteristics. However, it is alsoused as a protective layer for underlying CNT fabric layers 3422 or 3424or 3426 for all subsequent processing until patterning and passivationnear the end of the process flow.

Next, methods 3330 deposit a conductor layer on the surface of contactlayer 3428 as illustrated in structures 3420-1, 3420-2, and 3420-3 asshown in FIGS. 34D-1, 34D-2, and 34D-3, respectively, using knownindustry methods. Thicknesses may range from 5 nm to 500 nm for example.The term conductor may include metals, metal alloys, semiconductors,silicides, conductive oxides, various allotropes of carbon, and othermaterials, as described further above with respect to methods 3310.

Next, methods 3330 deposit a resist layer, expose and develop theresist, then etch to pattern array wires on the surface of contact layer3428 using known industry methods, forming top array wires 3430 asillustrated by plan view 3420 in FIG. 34C and in cross sections 3420-1,3420-2, and 3420-3 illustrated in FIGS. 34D-1, 34D-2, and 34D-3. Toparray wire 3430 width may be scaled over a large range: on the order of250 nm to on the order of 10 nm. Methods 3300 may be used to form arraywire 3440 widths of less than 10 nm.

Next, methods 3340 ion implant CNT fabric layer 3426 through contactlayer 3428 in exposed regions 3444 shown in cross section 3440illustrated in FIG. 34E. Ion implant 3442 methods are described furtherabove with respect to FIGS. 4C, 4D, and 4E. Ion implant 3442 formshigh-resistance (high-R) CNT fabric isolation regions 3454 between toparray wires 3430 as shown in cross section 3450 illustrated in FIG. 34F.High-R values may be in the hundreds of mega-Ohms or giga-Ohm range;that is forming essentially insulating regions, thereby eliminatingparasitic currents in the CNT fabric layer between top array wires. CNTswitching regions 3452 under top array wire 3430 are unchanged.

Next, methods 3350 deposit a first sacrificial layer using knownindustry methods. Examples of first sacrificial layer materials areSiO₂, SiN, Al₂O₃, TEOS, polyimide, HfO₂, TaO₅, combinations of theseinsulator materials, and other insulator materials. Various conductors,semiconductors, allotropes of carbon, or other materials as describedfurther above with respect to methods 3310 may also be used. Inaddition, various resists may also be used to form a first sacrificiallayer.

Then, methods 3350 planarize the first sacrificial layer to the topsurface of top array wires 3430 using known industry methods, formingfirst sacrificial layer 3462, as illustrated by cross section 3460illustrated in FIG. 34G. The top surface 3464 of cross section 3460includes the top surface of top array wires 3430 and the top surface offirst sacrificial layer 3462.

At this point in the process, CNT fabric layer 3426 has been transformedby ion implant 3442 into high-R CNT fabric isolation regions 3454 orleft as CNT switching regions 3452 as illustrated in FIGS. 34F and 34G.CNT switching regions 3452 are approximately F×l_(Y) in size, locatedunder top array wires 3430, and high-R CNT fabric isolation regions 3454are approximately F×l_(Y) in size, and located between top array wires3430.

In the continuing process described further below, CNT switching regionsF×l_(Y) along the Y-direction are transformed by another ion implantthrough contact layer 3428 and similar to ion implant 3442 describedfurther above, into high-R CNT fabric isolation regions of F×Fdimensions, alternating with F×F CNT switching regions that are leftunchanged. At the end of process flow, CNT switching regions of CNTfabric layer 3426 of approximately F×F minimum dimensions remain inregions of overlap between top array wires 3430 and bottom array wires3404. All other regions of CNT fabric layer 3426 in the memory arrayhave been transformed into high-R CNT fabric isolation regions by ionimplantation. These F×F minimum dimension CNT switching regions areformed by the intersection of array wires and sacrificial array wires ofF×l dimensions, without requiring the etching of minimum F×F shapes.

Next, methods 3360 deposit and planarize a second sacrificial layer onsurface 3464 illustrated in FIG. 34G using known industry methods.Examples of first sacrificial layer materials are SiO2, SiN, Al₂O₃,TEOS, polyimide, HfO2, TaO5, combinations of these insulator materials,and other insulator materials. Various conductors, semiconductors,allotropes of carbon, or other materials as described further above withrespect to methods 3310 may also be used. In addition, various resistsmay be used as well.

Next, methods 3360 deposit a resist layer on the top surface of thesecond sacrificial layer, expose and develop the resist, then etch toform sacrificial array masking wires 3502 illustrated in FIG. 35A onsurface 3464 (FIG. 34G) using known industry methods. The etch isselective to first sacrificial layer 3462 and top array wires 3430.Sacrificial array masking wires 3502 are aligned to, and positionedabove, bottom array wires 3404 and have approximately the samedimensions. Sacrificial array wire 3502 width may be scaled over a largerange: on the order of 250 nm to on the order of 10 nm. Methods 3300 maybe used to form sacrificial array masking wire 3502 widths of less than10 nm.

Then, methods 3360 etch (remove) exposed top array wires 3430 shown inplan view 3500 illustrated in FIG. 35A, selective to first sacrificiallayer 3462 and contact layer 3428, exposing the top surface of contactlayer regions 3504 as shown in plan view 3510 illustrated in FIG. 35B,and changing continuous top array wires 3430 to top array wire segments3430S shown in cross section 3520 along the X-direction as illustratedin FIG. 35C, using known industry methods. Cross section 3520corresponds to cross section EE′ shown in FIG. 35B. Cross section 3520shows sacrificial array masking wire 3502 in contact with the topsurface of top array wire segments 3430S, which are on top of contactlayer 3428, and above CNT switching region 3452 in CNT fabric layer3426. The combination of sacrificial array masking wire 3502 and toparray wire segments 3430S prevent a subsequent ion implant step shownfurther below in FIG. 36A from changing the resistance of CNT switchingregion 3452. High-R CNT fabric isolation region 3454 is already at ahigh resistance because of ion implant 3442 shown in FIG. 34E. And whilethe combination of sacrificial array masking wire 3502 and firstsacrificial layer 3462 may prevent a subsequent ion implant step fromreaching high-R CNT fabric isolation region 3454, this is not arequirement, and in fact can have the beneficial effect of furtherincreasing high-R CNT fabric isolation resistance values.

Cross section 3530 along the X-direction illustrated in FIG. 35D,corresponds to cross section FF′ shown in FIG. 35B, and shows firstsacrificial layer 3462 with exposed contact layer regions 3504 ofcontact layer 3428 as a result of applying methods 3360 describedfurther above. CNT switching regions 3452 may be converted to high-R CNTfabric isolation regions 3654 by ion implantation 3602 as describedfurther below with respect to FIGS. 36C and 36D.

Cross section 3540 along the Y-direction illustrated in FIG. 35E,corresponds to cross section GG′ shown in FIG. 35B, and shows thecombination of sacrificial array masking wire 3502 and top array wiresegments 3430S that protect (mask) underlying CNT fabric layer 3426regions from a subsequent ion implant step shown further below in FIG.36A. Exposed CNT fabric layer 3426 regions may be converted to high-RCNT fabric isolation regions by ion implantation as described furtherbelow with respect to FIGS. 36C and 36D.

Cross section 3550 along the Y-direction illustrated in FIG. 35F,corresponds to cross section HH′ shown in FIG. 35B, and showssacrificial array masking wires 3502 on the top surface of firstsacrificial insulator 3462. Underlying CNT fabric layer 3426 wasconverted to a high-R CNT fabric isolation region by ion implant 3442illustrated in FIGS. 34E and 34F. Subsequent ion implantation may reachunderlying 3426, which can have the beneficial effect of furtherincreasing high-R CNT fabric isolation resistance values.

At this point in the process, as described further below, a second ionimplant, ion implant 3602 through contact layer 3428, converts regionsof CNT fabric layer 3426 below exposed contact layer regions 3504, asshown in plan view 3510 illustrated in FIG. 35B, from CNT switchingregions to high-R CNT fabric isolation regions. After ion implant 3602,CNT switching regions 3452 of CNT fabric layer 3426 remain only inregions at the intersection of sacrificial array masking wires 3502 andtop array wire segments 3430S.

Methods 3370 ion implant the structure illustrated in plan view 3510illustrated in FIG. 35B as shown in FIGS. 36A, 36C, and 36E with ionimplant 3602. Ion implant 3602 is similar to ion implant 3442 describedfurther above. Ion implant methods are described further above withrespect to FIGS. 4C, 4D, and 4E.

FIG. 36A illustrates ion implant 3602 applied with respect to crosssection 3520, also shown in FIG. 35C. As shown in corresponding crosssection 3620 illustrated in FIG. 36B along the X-direction, CNTswitching regions 3452 in CNT fabric layer 3426 remain unchanged,protected by the combination of sacrificial array masking wire 3502 andtop array wire segment 3430S. High-R CNT fabric isolation regions 3454formed by ion implant 3442 (FIG. 34E) remains essentially unchanged byion implant 3602. If any ion implant 3602 dosage reaches high-R CNTfabric isolation region 3454, it can only have the beneficial effect offurther increasing high-R resistance values.

FIG. 36C illustrates ion implant 3602 applied with respect to crosssection 3530, also shown in FIG. 35D. As shown in corresponding crosssection 3630 illustrated in FIG. 36D along the X-direction, CNTswitching regions 3452 in CNT fabric layer 3426 are changed to high-Risolation regions 3654 in exposed regions 3504 between first sacrificiallayer 3462 openings by ion implant 3602 through contact layer 3428. CNThigh-R isolation regions 3454 formed by ion implant 3442 (FIG. 34E)remains essentially unchanged by ion implant 3602. If any ion implant3602 dosage reaches high-R CNT fabric isolation region 3454, it can onlyhave the beneficial effect of further increasing high-R isolationresistance values.

FIG. 36E illustrates ion implant 3602 applied with respect to crosssection 3540, also shown in FIG. 35E. As shown in corresponding crosssection 3640 illustrated in FIG. 36F along the Y-direction, CNTswitching regions 3452 in CNT fabric layer 3426 are left unchanged,protected at the intersection of sacrificial array masking wires 3502and top array wire segments 3430S. However, in unprotected regions 3504,switching regions in CNT fabric layer 3426 are changed from CNTswitching regions 3452 to high-R CNT fabric isolation regions 3654 byion implant 3602 through contact layer 3428.

At this point in the process, as described further below, sacrificialarray masking wires 3502, formed as described further above by etching asecond sacrificial layer, may be removed (etched) selective to contactlayer 3428, top array wire segments 3430S, and first sacrificial layer3462. Exposed regions of contact layer 3428 are defined in theX-direction by edges of first sacrificial layer 3462 openings separatedby a distance F, and in the Y-direction by edges of top array wiresegments 3430S separated by a distance F. A damascene process may beused to fill the exposed regions with a conductor that interconnects toparray wire segments 3430S, thereby converting top array wire segments3430S to top array wires 3730 of dimensions F×l_(Y) as illustrated inFIG. 37D further below. First sacrificial layer 3462 may then be removed(etched), and then exposed regions of contact layer 3428 may also beremoved as well. An insulating layer is then deposited and planarized toprotect the underlying cross point memory array, all as describedfurther below.

Methods 3380 remove (etch) sacrificial array masking wires 3502,selective to contact layer 3428, first sacrificial layer 3462, and toparray wire segments 3430S shown in FIGS. 35B, 35C, 35E, and 35F usingknown industry methods, which results in the structures illustrated byplan view 3700 shown in FIG. 37A and cross section 3720 in theY-direction as shown in FIG. 37B, corresponding to cross section JJ′shown in FIG. 37A. Openings 3704 expose sections of the top surface ofcontact layer 3428 as shown in FIGS. 37A and 37B. The dimensions ofopenings 3704 are defined in the X-direction by edges of firstsacrificial layer 3462 openings separated by a distance F, and in theY-direction by edges of top array wire segments 3430S separated by adistance F.

Next, methods 3390 deposit a conductor layer which penetrates theopening 3704 and contacts exposed regions of contact layer 3428, alsocovering and contacting top array wire segments 3430S. Next, theconductor layer is planarized to the top surfaces of first sacrificialinsulator 3462 and top array wire segments 3430S using known industrydamascene process methods, forming continuous top array wire 3730 shownin cross section 3740 in the Y-direction as illustrated in FIG. 37C.Plan view 3760 illustrated in FIG. 37D also show top array wires 3730and exposed regions of contact layer 3428 between top array wires 3730.CNT switching region 3452, formed by ion implant 3442 in CNT fabriclayer 3726, is positioned at the intersection of top array wire 3730 andbottom array wires 3404. High-R CNT fabric isolation region 3654, formedby ion implant 3602, isolates adjacent CNT switching regions 3452 asillustrated in FIG. 37C

Next, methods 3390 etch (remove) exposed regions of contact layer 3428using top array wires 3730 as a masking layer exposing the top surfaceof CNT fabric layer 3426 as shown in plan view 3780 illustrated in FIG.37E. Methods of etching metals and insulators without damaging CNTs inCNT fabric layers are described in the referenced patents and patentpublications further above with respect to methods 3320. The top surfaceof CNT fabric layer 3426 is exposed between top array wires 3730.

Next, methods 3390 deposit and planarize an insulating layer forminginsulator 3802 using industry methods to complete the cross point memoryarray 3800 illustrated in plan view in FIG. 38A. A passivation layer maybe deposited on the top surface of plan view 38A. Alternatively, themethods 3390 planarization step may not planarize the insulating layerto the top surface of array wires 3730, thereby forming both ainsulating layer between array lines 3730 and a passivation layer abovearray wires 3730. Cross point memory array 3800 and other structuresshown in various cross sections described further below correspond tocross point sub-array 2120 shown schematically in FIG. 21. Multiplecross point memory arrays 3800 may be fabricated on a chip to form crosspoint memory array 2100 illustrated schematically in FIG. 21. In thisexample, CNT fabric layer 3426 was used and the resulting NV CNTresistive block switches include an integrated diode switchcorresponding to cross point memory array 2300, which includes a selectdiode in 1-RS cell 2350, both shown schematically in FIGS. 23A and 23B,respectively. Select diode 1-RS cell 2380 illustrated in FIG. 23C may beused instead of 1-RS cell 2350.

Cross section 3810 along the X-direction illustrated in FIG. 38B,corresponds to cross section KK′ shown in FIG. 38A, and shows patternedcontacts 3804 between top array wires 3730 and underlying CNT fabriclayer 3426. CNT switching regions 3452 are at the intersection of toparray wire 3730 and bottom array wire 3404 on substrate 3402. High-R CNTfabric isolation regions 3454, formed by ion implant 3442, preventcurrent flow between adjacent cell CNT switching regions 3452 of NV CNTresistive switches 3812 through CNT fabric layer 3426. NV CNT resistiveblock switch 3812 is illustrated in cross section 3810 with a minimumdimension F in the X-direction. NV CNT resistive block switch 3812corresponds to resistive change memory element 450 illustrated anddescribed further above with respect to FIG. 4B.

Cross section 3820 along the Y-direction illustrated in FIG. 38C,corresponds to cross section LL′ shown in FIG. 38C, and shows patternedcontact 3804 between top array wire 3730 and underlying CNT fabric layer3426. CNT switching regions 3452 are at the intersection of top arraywire 3730 with underlying contact layer 3804 and bottom array wire 3404on substrate 3402. High-R CNT fabric isolation regions 3654, formed byion implant 3602, prevent current flow between adjacent cell CNTswitching regions 3452 of NV CNT resistive switches 3812 through CNTfabric layer 3426. NV CNT resistive block switch 3812 is illustrated incross section 3820 with a minimum dimension F in the Y-direction. NV CNTresistive block switch 3812 corresponds to resistive change memoryelement 450 illustrated and described further above with respect to FIG.4B.

Cross section 3830 along the X-direction illustrated in FIG. 38D,corresponds to cross section MM′ shown in FIG. 38D, and shows patternedcontacts 3804 between top array wires 3730 and underlying CNT fabriclayer 3426. High-R CNT fabric isolation regions 3654 and 3454 alternatealong the length of CNT fabric 3426 and prevent leakage between cell CNTswitching regions 3452 of NV CNT resistive switches 3812.

Cross section 3840 along the Y-direction illustrated in FIG. 38E,corresponds to cross section NN′ shown in FIG. 38E, and shows a crosssection of insulator 3802 on the top surface of CNT fabric layer 3426.CNT fabric layer 3426 is a high-R CNT fabric isolation region 3454formed by implant 3442 along the entire length. High-R CNT fabricisolation region 3454 prevents leakage between cell CNT switchingregions 3452 of NV CNT resistive switches 3812.

Methods 3300 and corresponding cross point memory array 3800 illustratedin plan view FIG. 38A and cross sections illustrated in FIGS. 38B-38Edescribe methods of fabrication and corresponding structures that may beused to implement cross point sub-arrays 2120 and cross point memoryarray 2300 illustrated schematically in FIGS. 21 and 23, respectively.Cross point memory array 3800 enables vertical current flow betweenintersecting top array wires 3730 and bottom array wires 3404, whilepreventing lateral current flow in any direction. Multiple cross pointmemory arrays 3800 may be fabricated in a chip to form cross pointmemory array 2100 illustrated schematically in FIG. 21 and cross pointmemory array 2300 illustrated in FIG. 23A. For minimum dimensions F=15nm, cell periodicity=2F=30 nm. For 10,000 bits per array line, forexample, then array lines are approximately 300 μm in length. TheX-direction and Y-direction array lines may have different bits per bitlines. In this example, assuming the same number of bits per array line,then bottom array wires 3404 illustrated in FIG. 34A are F=15 nm wideand l_(X)=300 μm in length. Bottom array wire 3404 corresponds toX-direction array wire 2125 illustrated in FIG. 21. Also in thisexample, assuming the same number of bits per array line, then top arraywires 3430 illustrated in FIG. 34C are F=15 nm wide and l_(Y)=300 μm inlength. Top array wire 3430 corresponds to Y-direction array wire 2130illustrated in FIG. 21. Using methods (of fabrication) 3300, integratedNV CNT resistive block switches 3812 illustrated in FIGS. 38B and 38C,have an X-direction dimension of F=15 nm and Y-direction dimension F=15nm. The NV CNT resistive block switch dimensions of 15×15 nm were formedby the intersection of overlapping array wires having dimensions of 15nm by 300 μm, without requiring the formation of 15×15 nm shapes asdescribed further above. Methods 3300 are compatible with scalable crosspoint memory arrays to smaller dimensions.

For example, cross point memory array 3800 illustrated in plan view FIG.38A and cross sections illustrated in FIGS. 38B-38E may be scaled toF=10 nm. For minimum dimensions F=10 nm, cell periodicity=2F=20 nm. For10,000 bits per array line, for example, then array lines areapproximately 200 μm in length. The X-direction and Y-direction arraylines may have different bits per bit lines. In this example, assumingthe same number of bits per array line, then bottom array wires 3404illustrated in FIG. 34A are F=10 nm wide and l_(X)=200 μm in length.Also in this example, assuming the same number of bits per array line,then top array wires 3430 illustrated in FIG. 34C are F=10 nm wide andl_(Y)=200 μm in length. Using methods (of fabrication) 3300, integratedNV CNT resistive block switches 3812 illustrated in FIGS. 38B and 38C,have an X-direction dimension of F=10 nm and Y-direction dimension F=10nm. The NV CNT resistive block switch dimensions of 10×10 nm were formedby the intersection of overlapping array wires having dimensions of 10nm by 200 μm, without requiring the formation of 10×10 nm shapes asdescribed further above. Methods 3300 are compatible with scalable crosspoint memory arrays to minimum dimensions less than 10 nm.

While methods 3300 have been used to form cross point memory array 3800using CNT fabric layers, conductors, and insulators to form NV CNTresistive block switch 3812 memory cells, methods 3300 may also beapplied to integrate graphic layers and buckyball layers to form crosspoint resistive change memory cells illustrated further above withrespect to FIGS. 1D, 1E, 5, and 6 described further above. For example,NV graphitic resistive block switch 540 illustrated in FIG. 5D, whichincludes switch graphitic layer 544 and diode graphitic layer 514, maybe formed instead of NV CNT resistive block switch 3812 illustrated inFIGS. 38B and 38C. Also, for example, NV buckyball resistive blockswitch 640 illustrated in FIG. 6D, which includes switch buckyball layer644 and diode buckyball layer 614, may be formed instead of NV CNTresistive block switch 3812 illustrated in FIGS. 38B and 38C.

Combinations of CNT fabric layers, graphitic layers, and buckyballlayers illustrated in FIGS. 5 and 6 may also be used to form cross pointmemory cells. For example, NV CNT resistive block switch 520 illustratedin FIG. 5B, which includes switch nanotube fabric layer 524 and diodegraphitic layer 514, may be formed instead of NV CNT resistive blockswitch 3812 illustrated in FIGS. 38B and 38C. Also, for example, NV CNTresistive block switch 620 illustrated in FIG. 6B, which includes switchnanotube fabric layer 624 and diode buckyball layer 614, may be formedinstead of NV CNT resistive block switch 3812 illustrated in FIGS. 38Band 38C, Other combinations, not shown, of CNT fabric layers, graphiticlayers, and buckyball layers may also be used.

Methods 3300 may also be used to form cross point phase change memorycells using phase change material, cross point metal-oxide memory cells,and other cross point memory cells using still other materials.

Methods 3300 result in NV CNT resistive block switches 3812 in which CNTswitching regions 3452 are self-aligned in the X-direction to top arraywires 3730. However, NV CNT resistive block switches 3812 CNT switchingregions 3452 are not self-aligned to bottom array wires 3404 in the Ydirection because methods 3300 use sacrificial array masking wires 3502illustrated in FIG. 35B, aligned to, and positioned above, bottom arraywires 3404. NV CNT resistive block switches 3812 illustrated in theY-direction in FIG. 38C are shown with aligned sacrificial array maskingwires 3502 and bottom array wires 3404. Cross section 3900 illustratedin FIG. 39 shows NV CNT resistive block switches 3912 in which CNTswitching regions 3452 and corresponding high-R CNT fabric isolationregions 3654 are misaligned by an amount Δ relative to bottom arraywires 3404. For example, Δ may represent a misalignment of +−0.3F. ForF=15 nm, then Δ=4.5 nm. For F=10 nm, then Δ=3.0 nm. Misalignment Δ doesnot change cross point memory array 3800 density (dimensions).Misalignment Δ of 0.3F reduces the bottom surface area contact of CNTswitching region 3452 with bottom array wires 3404 from 100% to 70%. Thetop surface of CNT switching region 3452 coverage remains 100% becauseof self-alignment with respect to top array wires 3730. NV CNT resistiveblock switch 3912 electrical characteristics remain essentially the sameas those of NV CNT resistive block switch 3812. US Pub. 2008/0160734shows NV CNT resistive block switches with full and partial coverage ofsurfaces having essentially the same electrical characteristics.

Forming Logic Functions with Cross Point Arrays, Programmable ArrayLogic (PAL), Diode-Resistor Logic (DRL), and Field Programmable GateArrays (FPGAs), and ESD Protect Devices

At this point in the specification, the focus is changed fromnonvolatile memory to configurable logic, i.e. resistive change logicelements using the same underlying technology used in memory: carbonnanotubes, graphitic carbon, and buckyballs and correspondingfabrication methods. Cross point arrays for signal routing, voltagedistribution, and power distribution is described with respect to FIGS.40 and 41; a programmable logic function (PAL) is described with respectto FIG. 42. In this example, a cross point array in a memory mode isused to configure cross point array bits used to generate logicfunctions, and the logic function is generated in logic mode.Optionally, the cross point array in a memory mode may be used as a NVembedded memory; combinatorial diode-resistor logic (DRL) functions areshown as DRL AND gates and DRL OR gates with respect to FIGS. 43A and43B; Field programmable gate arrays (FGPAs) are formed usingcombinations of configurable nonvolatile select circuits, configurablelogic blocks (CLBs) using DRL logic gates and cross point arraylook-up-tables (LUTs), and programmable switch matrices (PSM) to routesignals between CLBs to form full-function FPGA logic are described withrespect to FIGS. 44-47; and ESD protect devices are described withrespect to FIG. 48.

Cross Point Arrays Used for Signal Routing and/or Voltage or PowerDistribution

FIG. 40 illustrates a plan view of cross point array 4000 that may beused to route signals, distribute power supply voltages, and distributepower along and between buses, referred to as wires. Cross point array4000 corresponds structurally to cross point array 120 illustrated inFIG. 1B-1, with corresponding cross sections 1B-2, and 1B-3.Two-terminal NV CNT resistive block switches 130-1, 130-2, 130-3, and130-4 may used to selectively connect bottom wires 122 and 124 with topwires 126 and 128. Referring to FIGS. 1B-1, 1B-2, and 1B-3, the emphasisis on maximizing cross point array density with cross point switches ofF×F minimum dimensions. However, referring to FIG. 40, the emphasis ison signal and/or voltage and/or power distribution with low voltagedrop, and hence low ON-state R_(ON) resistance values for NV CNTresistive block switches. Therefore, dimensions may be much larger thanminimum dimensions F because low resistance values require many moreparallel conductive paths in the resistive change cross point arrayswitching elements. R_(ON) resistance values may vary depending on theapplication. By way of examples: R_(ON) in the range of 1-100Ω for someapplications, 100-1,000Ω, and 1,000-10,000Ω for other applications.Hence, instead of F=10 nm dimensions, for example, NV CNT resistiveblock switch dimensions may be 100×100 nm, 1×1 μm, 10×10 μm, 100×100 μm,or have still other dimensions, as needed to meet desired R_(ON)resistance values. Nonvolatile cross point switches may be formed withNV CNT resistive block switches 130-1, 130-2, 130-3, and 130-4 asillustrated in FIGS. 1B and 1C. However, these NV cross point switchesmay also be formed with NV graphitic resistive block switch 162illustrated in FIG. 1D, or NV buckyball resistive block switch 182illustrated in FIG. 1E.

Referring to FIG. 40, cross point array 4000 may perform a routingfunction. In the example illustrated in FIG. 40, NV CNT resistive blockswitches 130-1, 130-2, 130-3, and 130-4 are all in a high resistanceR_(OFF) RESET state and cross point array 4000 has not been configuredfor signal routing. For example, R_(OFF) may be in the Giga-Ohm range asillustrated in FIG. 15. Hence, signal propagation, voltage distribution,or power distribution remains within individual wires, with nopropagation or distribution between wires. By way of example,propagation/distribution 4010 remains within bottom wire 122,propagation/distribution 4020 remains within bottom wire 124,propagation/distribution 4030 remains within top wire 126, andpropagation/distribution 4040 remains within top wire 128.

Referring to FIG. 41A, configured cross point array 4100 illustrated inFIG. 41A has been configured such that NV CNT resistive block switch130-2 is in a low resistance R_(ON) SET state interconnecting bottomwire 122 and top wire 128 through a resistance in the range of 1-10,000Ohms, selected for the required application, such as signal propagationand/or voltage and/or power distribution as described further above. Allother NV CNT resistive block switches remain in a high resistance state.When configuring specific NV CNT resistive cross point switches forrouting purposes, there are no undesired interactions with adjacentswitches that can result in parasitic losses (sneak current paths) suchas illustrated in FIG. 2A, for example. This is because the state ofadjacent switches is not modified during the configured switchoperation. Accordingly, NV CNT resistive block switches may benear-Ohmic, for example, enabling bidirectional signal, voltage, andpower flow. If desired, highly non-linear switches may be formed, andmay include a series diode for uni-directional signal, voltage, andpower flow. However, in these examples, near-Ohmic NV CNT resistiveblock switches are assumed. Applied voltages and currents used to writeNV CNT resistive block switches, switching them between low resistanceSET and high resistance RESET states, is as described further above withrespect to FIG. 19.

Referring to FIG. 41A, configured cross point array 4100 withinterconnected bottom wire 122 and top wire 128 connected by NV CNTresistive block switch 130-2 results in propagation/distribution 4105.Propagation/distribution 4105 flows in both bottom array wire 122 andtop array wire 128. Propagation/distributions 4020 and 4030 flow inbottom wire 124 and top wire 126, respectively, as also illustrated inFIG. 40, and remain unchanged.

Referring to FIG. 41B, configured cross point array 4120 has beenconfigured such that NV CNT resistive block switch 130-4 is in a lowresistance R_(ON) SET state and interconnects bottom wire 124 and topwire 128 through a resistance in the range of 1-10,000 Ohms, selectedfor the required application, such as signal propagation and/or voltageand/or power distribution. NV CNT resistive block switch 130-4 enablespropagation/distribution 4125 of signal, voltage, or power through NVCNT resistive block switch 130-4 and remains within individual bottomwire 124 and top wire 128. All other NV CNT resistive block switchesremain in a high resistance state. Propagation/distributions 4010 and4030 flow in bottom wire 122 and top wire 126, respectively, as alsoillustrated in FIG. 40, and remain unchanged.

Referring to FIG. 41C, configured cross point array 4140 has beenconfigured such that NV CNT resistive block switches 130-2 and 130-3 arein a low resistance R_(ON) SET state and interconnect bottom wire 122and top wire 128, and bottom wire 124 and top wire 126, respectively,through a resistance in the range of 1-10,000 Ohms, selected for therequired application, such as signal propagation and/or voltage and/orpower distribution. NV CNT resistive block switches 130-2 and 130-3enable propagation/distributions 4145 and 4150, respectively, of signal,voltage, or power. Propagation/distribution 4145 flows through NV CNTresistive block switch 130-2 and remains within individual bottom wire122 and top wire 128. Propagation/distribution 4150 flows through NV CNTresistive block switch 130-3 and remains within individual bottom wire124 and top wire 126. All other NV CNT resistive block switches, in thisexample NV CNT resistive block switches 130-1 and 130-4, remain in ahigh resistance state.

Referring to FIG. 41D, configured cross point array 4160 has beenconfigured such that NV CNT resistive block switches 130-2 and 130-4 arein a low resistance R_(ON) SET state and interconnect top wire 128 withbottom wires 122 and 124, respectively, through a resistance in therange of 1-10,000 Ohms, selected for the required application, such assignal propagation and/or voltage and/or power distribution. NV CNTresistive block switches 130-2 and 130-4 enable propagation/distribution4165 of signal, voltage, or power. Propagation/distribution 4165 flowsthrough NV CNT resistive block switches 130-2 and 130-4 and remainswithin individual top wire 128 and bottom wires 122 and 124. All otherNV CNT resistive block switches, in this example NV CNT resistive blockswitches 130-1 and 130-3, remain in a high resistance state.Propagation/distribution 4030 flows in top wire 126, as also illustratedin FIG. 40, and remain unchanged.

Other configured cross point arrays may also be formed using theprinciples illustrated with respect to FIGS. 41A, 41B, 41C, and 41D.

Examples of configured cross point arrays that enable variouspropagation/distribution combinations of signal propagation and/orvoltage and/or power distribution have been described further above withrespect to FIGS. 40 and 41. However, configured cross point arrays mayalso be used in various circuit configurations. For example, configuredcross point array 4160 may be used as a voltage divider. NV CNTresistive block switches may be switched to various R_(ON) SET-stateresistance values over a wide range of resistance as illustrated in U.S.Pat. No. 8,102,018. For example, a voltage divider network may be formedthat includes NV CNT resistive block switch 130-2 to an R_(ON) value ofR1 between bottom wire 122 and top wire 128, and NV CNT resistive blockswitch 130-4 set to an R_(ON) value of R2 between top wire 128 andbottom wire 124. An input voltage V_(IN) is applied to bottom wire 122with respect to a common ground reference, and bottom wire 124 isconnected to ground. Voltage divider network output V_(OUT) on top wire128 results from the ratio of R_(ON) resistance values R1 and R2 suchthat V_(OUT)=[R2/(R1+R2)]V_(IN). Values of R1 and R2 may be setindependently over a large range of resistance values. By way ofexample, if R1=150 kΩ and R2=50 kΩ, then voltage divider output voltageV_(OUT)=0.25 V_(IN); if R1=150Ω and R2=150 kΩ, then V_(OUT)=0.50 V_(IN);and if R1=50 kΩ and R2=150 kΩ, then V_(OUT)=0.750 V_(IN). The voltagedivider output voltage V_(OUT) may be set to any other multiple ofV_(IN), generating various analog voltage values.

In some cases, it is desirable to have multiple voltage divider outputvoltage V_(OUT) values simultaneously available. A way of achieving thisis to have three configured cross point arrays with differentcombinations of R1 and R2. For example, a first configured cross pointarray 4160 with R1=150 kΩ and R2=50 kΩ with V_(OUT)=0.25 V_(IN); and asecond configured cross point array 4160 with R1=150 kΩ and R2=150 kΩwith V_(OUT)=0.50 V_(IN); and a third configured cross point switch 4160with R1=50 kΩ and R2=150 kΩ with V_(OUT)=0.75 V_(IN). Alternatively,three different voltage divider output voltage V_(OUT) values may beavailable simultaneously from the same configured cross point array ifthere are more total cross point switches and top and bottom wiresavailable.

Cross Point Array-Based Programmable Array Logic (XP-PAL)

Cross point array-based programmable array logic (XP-PAL) 4200illustrated in FIG. 42 may be configured as a memory to programindividual bits to form logic functions as described further below.Then, XP-PAL 4200 is operated in a logic mode to generate the logicfunction corresponding to the programmed memory bits. Optionally, XP-PAL4200 may be used as embedded memory function.

XP-PAL 4200 uses a configuration controller 4202 with input INP1 andmode select 4230 output to activate an XP-PAL 4200 logic mode ofoperation after programmable/reprogrammable AND array 4205 bits havebeen programmed. Alternatively, mode select 4230 may activate a memorymode. When in memory mode, XP-PAL 4200 logic functions are disabled, andXP-PAL 4200 may be used instead as an embedded NRAM memory with a memorycontrol function, word decoders and drivers, bit decoders and drivers,and latch and I/O functions. Memory operation is similar to descriptionswith respect to FIG. 19. When in memory mode, cells may be programmed orreprogrammed to implement new XP-PAL 4200 logic functions. Horizontalarray lines each form a single product term such as PT1 when XP-PAL 4200operates in a logic mode or a bit line such as BL1 when operating in amemory mode. Vertical array lines may form a single logic input in alogic mode such as input logic IL1 or form a word line such as word lineWL1 when operating in a memory mode. Logic or memory modes of operationare controlled by configuration controller 4202 based on input(s) INP1by providing a low voltage (near ground) mode select signal 4230 forXP-PAL operation or by providing a high voltage (at or near V_(DD)) formemory write SET or RESET operations. SET results in a NV resistiveswitch low resistance state and RESET results in a NV resistive switchhigh resistance state as described with respect to FIG. 19.

In a logic operating mode, XP-PAL 4200 logic input circuits 4210 drivevertical array lines corresponding to logic variables A, A_(C), B, andB_(C), while feedback lines 3570 and 3575 provide logic output O1 thatprovides logic variable C and logic output O2 that provides logicvariable D, respectively, as inputs. True and complement logic variablesmay be represented as A and A_(C); B and B_(C); C and C_(C); and D andD_(C), respectively. The combination of logic input circuits 4210 drivecathodes of integrated diode 4207B illustrated in cell 4207 as shown inFIG. 42, and logic states are stored as a nonvolatile resistance valuesin NV resistive switches 4207A connected to product term (PT) arraylines. 1-RS cell 4207 corresponds to 1-RS cell 2380 illustrated in FIG.23C. 1-RS cell 2380, formed between terminals 1 and 2, includes NVresistive switch 2385, corresponding to NV resistive switch 4207A andintegrated diode 2390, corresponding to integrated diode 4207B. Theanode of integrated diode 4207B is connected to a first terminal of NVresistive switch 4207A. Terminal 1 corresponds to the cathode ofintegrated diode 4207B and terminal 2 corresponds to a second terminalof NV resistive switch 4207A. Cell 4207 is formed between terminals 1and 2. Terminals 2 connect a second terminal of NV resistive switches4207A to horizontal array lines corresponding to product terms such asPT1, PT2, PT3, and PT4. Terminals 1 connect the cathodes of integrateddiodes 4207B to logic input lines IL1, IL2 . . . , IL8. In a nanotubeprogrammable array logic (NPAL) operating mode, XP-PAL 4200 operatingvoltage swings are kept below switching voltage level, less than orequal to 2 volts for example, with switching voltages for write modesSET and RESET typically 3 volts or higher. In a NPAL operating mode,each of the product terms is connected to a pull up PFET deviceconnected to a power supply voltage V. Product term lines such as PT1 isin a high voltage state prior to the activation of input logic signals.In this example, PT1 remains in a high voltage state for any combinationof inputs A, A_(C), B, B_(C), C, C_(C), D, and D_(C) if all NV resistiveswitches 4207A are in an OFF or high resistance state so no current canflow in cell 4207. Dotted circles in FIG. 42 indicate NV resistiveswitches 4207A that are in a low resistance SET state in this example.Nonvolatile cross point switches may be formed with NV CNT resistiveblock switches 130-1, 130-2, 130-3, and 130-4 as illustrated in FIGS. 1Band 1C. However, these NV cross point switches may also be formed withNV graphitic resistive block switch 162 illustrated in FIG. 1D, or NVbuckyball resistive block switch 182 illustrated in FIG. 1E. Nonvolatilecross point switches may also be formed with resistive change memoryelements illustrated in FIGS. 4, 5, 6, and 7.

In operation, in the case of product term PT4, the PT4 voltage level isV prior to input logic activation. However, if terminal 1 of integrateddiode 4207B receives a low voltage such as zero volts, for example, fromlogic input B_(C), then current flows through the corresponding cell andthe corresponding pull up PFET, and PT4 voltage drops to a low voltagebecause the NV resistive switch in the cell between PT4 and logic inputB_(C) is in a low resistance state. However, if logic input B_(C) is ata high voltage, such as 2 volts, the corresponding integrated diode isback biased and no current flows, and product term PT4 remains atvoltage V. Product term PT3 high or low voltage value depends on thestate of the NV resistive switch in the cell at the intersection of PT3,and logic input C, and corresponds to the behavior of PT4 as describedfurther above.

In operation, product term PT2 may be activated depending on the stateof two NV resistive switches and corresponding logic input levels.Product term PT2 is also at voltage V prior to logic input circuit 4210activation. In the case of product term PT2, NV NT block switches at twocell locations, a first cell at the intersection of PT2 and B_(C) and asecond cell at the intersection of PT2 and D_(C). If either the firstcell is selected or the second cell is selected, PT2 transitions fromvoltage V to a low voltage such as a reference voltage at or nearground; and if both the first and second cells are selected, PT2 is alsoat a low voltage near ground.

In operation, each of the product terms PT1, PT2, PT3, and PT4 inprogrammable AND array 4205 correspond to the combination of all inputsignals on input lines (IL1-IL8) connected to the terminals 1 of theintegrated diodes 4207B and the ON (low resistance) or OFF (highresistance) states of the corresponding NV resistive block switches4207A in series as described in the examples described further above.Signal voltages on product terms PT1 and PT2 pass through mode selectFETs and form inputs to two-terminal OR circuit 4250 whose output drivesD-flip flop 4260. The output of D-flip flop 4260 is logic output O1.Product terms PT3 and PT4 pass through mode select FETs and form inputsto two-terminal OR circuit 4255 whose output drives D-flip flop 4265.The output of D-flip flop 4265 is logic output O2. Logic outputs O1 andO2 are fed back as logic inputs to programmable/reprogrammable AND array4205 as described further above. D-flip flops 4260 and 4265 compensatefor any voltage drops through integrated diodes in the array. OR gatesmay be formed using MOSFETs, or may also be formed using diode-resistorlogic as described further below with respect to FIGS. 43A and 43B.

When configuring or reconfiguring the cells inprogrammable/reprogrammable AND array 4205, configuration controller4202 mode select 4230 output transitions to a high voltage (V_(DD) forexample) and turns OFF corresponding FETs that enable/disable productterms PT1 and PT2 to the inputs of two terminal OR gate 4250 and productterms PT3 and PT4 to the inputs of two terminal OR gate 4265. FETtransfer devices that enable/disable connections between memory modeword decoders and WL drivers 4215 with inputs INP2 and dual functioninput lines/word lines such as IL1/WL1, IL2/WL2, IL3/WL3, IL4/WL4,IL5/WL5, IL6/WL6, IL7/WL7, and IL8/WL8 are turned ON. Also, PFET pull updevices connected to dual function product term line/bit lines such asPT1/BL1, PT2/BL2, PT3/BL3, and PT4/BL4 are turned OFF and FET transferdevices that enable/disable connections between memory mode bit decodeand BL drivers, and latch & I/O circuits 4220 with input INP3 and dualfunction product terms/bit lines such as PT1/BL1, PT2/BL2, PT3/BL3, andPT4/BL4 are turned ON. While FET transfer devices illustrated in FIG. 42have shown NFET transfer devices, PFET transfer devices may be usedinstead, as well as CMOS transfer devices using both NFET and PFET.

Programming/reprogramming of programmable/reprogrammable AND array 4205cells has been described in terms of an NRAM® operating modes. Thisapproach uses some additional circuits such as memory mode word decodersand WL drivers 4215 and memory mode bit decoders and BL drivers, andlatch & I/O circuits 4220 for example to simplify cellprogramming/reprogramming, and also to provide an embedded NRAM functionoption. However, it is possible to program/reprogram cells using onlythe XP-PAL 4200 logic input, output, and timing control circuits. Suchan alternative approach requires more complex programs/programmingmethods.

Diode-Resistor Logic (DRL) Circuits

Diode-resistor logic (DRL) is an old technology as described for examplein the reference: Frank Sterrett Davidson, “Design for a Diode-resistorLogic Circuit Family”, George Washington University, 1967. A summary ofdiode-resistor logic operation is described with respect to FIG. 43A andFIG. 43B. Until recently, diodes have been formed with semiconductormaterials such as Si, Ge, and many combinations of semiconductormaterials such GaAs, and have typically been PN diodes, althoughSchottky diodes have been used as well. Resistors may be formed ofconductors, semiconductors, doped oxides, and other materials. However,the advent of nanotechnology using materials such as carbon-based diodematerials has revived interest in diode-resistor logic.

Referring to FIG. 43A, diode-resistor logic (DRL) OR gate 4300 isillustrated with two voltage inputs IN1 and IN2 and a logic output O.Many more diode inputs may be used (not shown). IN1 is connected to theanode of diode 4310, IN2 is connected to the anode of diode 4315, andthe cathodes of both diodes are connected to output node 4320. Resistor4325 is connected to node 4320 and is also connected to a common lowreference voltage; typically ground (zero volts).

In operation, IN1 and IN2 can swing between ground and power supplyV_(PS), although a voltage drop through a diode in a preceding stage maylower the total swing by the amount of a diode forward voltage dropV_(D), typically in the range of 0.3-0.6 volts for example. If both IN1and IN2 are at ground for example, then no current flows and resistor4325 holds the output voltage O at ground, approximately zero volts inthis example. However, if either IN1 or IN2 is at V_(PS), then currentflows through resistor 4325 and the output voltage O=V_(PS)−V_(D). Byway of example, if V_(PS)=3.5 V. and diode forward voltage drop isV_(D)=0.5 V., then V_(OUT)=3.0 V.

Still referring to FIG. 43A, assigning logic bit “0” to zero volts andlogic bit “1” to V_(PS), or V_(PS)−V_(D), then logic table 4330illustrates all combinations of IN1 and IN2 expressed as a correspondinglogic bit “0” or corresponding logic bit “1”, and V_(OUT) is alsoexpressed as a corresponding logic bit. Logic table 4330 corresponds toan OR logic function, illustrating that the corresponding circuitgenerates an OR logic function for DRL OR gate 4300.

Referring to FIG. 43B, diode-resistor logic (DRL) AND gate 4350illustrated with two voltage inputs IN1 and IN2 and a logic output O.Many more diode inputs may be used (not shown). IN1 is connected to thecathode of diode 4360, IN2 is connected to the cathode of diode 4365,and the anodes of both diodes are connected to output node 4370.Resistor 4375 is connected to node 4370 and is also connected to powersupply voltage V_(PS).

In operation, IN1 and IN2 can swing between ground and power supplyV_(PS), although a voltage drop through a diode in a preceding stage maylower the total swing by the amount of a diode forward voltage dropV_(D), typically in the range of 0.3-0.6 volts for example. If either,or both, N1 and IN2 are at ground for example, then current flowsthrough resistor 4375 and the output voltage O at approximately zerovolts; actually, output voltage O is at V_(D), the forward diode voltagedrop, so if V_(D)=0.5 volts for example, then output O=0.5 V. However,if both IN1 and IN2 are at V_(PS), no current flows through resistor4375 and the output voltage V_(OUT)=V_(PS). By way of example, ifV_(PS)=3.5 V. then V_(OUT)=3.5 V.

Still referring to FIG. 43B, assigning logic bit “0” to zero volts orV_(D) and logic bit “1” to V_(PS), then logic table 4380 illustrates allcombinations of IN1 and IN2 expressed as a corresponding logic bit “0”or corresponding logic bit “1”, and output O is also expressed as acorresponding logic bit. Logic table 4380 corresponds to an AND logicfunction, illustrating that the corresponding circuit generates an ANDlogic function for DRL AND gate 4350.

Carbon-diode diode-resistor logic (CD-DRL) gates may be formed by usingcarbon-based diode materials. Examples of carbon-based diode materialsare diode CNT fabric layers, diode graphitic layers, and/or diodebuckyball layers described in detail further above with respect to FIGS.4F-4H, 5E-5G, and 6E-6G, respectively. Structures, fabrication, andoperation are described for various carbon-based diode examples. CD-DRLgates may be formed by using carbon-based diodes illustrated in FIGS.4F-4H, 5E-5G, and 6E-6G as diodes 4310, 4315, 4360, and 4365 illustratedin FIGS. 43A and 43B. Resistors 4325 and 4375, also illustrated in FIGS.43A and 43B, respectively, may continue to be formed of conductors,semiconductors, doped oxides, and other materials. However, carbon-basedresistors, for example carbon nanotube resistors fabricated frompatterned carbon nanotube fabrics may be formed and used as illustratedin U.S. Pat. No. 7,365,632 hereby incorporated by reference in itsentirety. Patterned graphitic layers, or patterned buckyball layers, mayalso be used to form resistors. The combination of carbon-based diodesand carbon-based resistors to form CD-DRL OR and AND logic gates may beused as logic families. Such CD-DRL gates integrate well with arraywires, including multiple stacked levels of array wires, because thesegates do not have to be in an underlying semiconductor substrate forexample.

Referring to carbon-based diodes 470 and 480 illustrated in FIGS. 4F and4G, respectively, carbon-based diodes 470 and 480 are formed asSchottky-type diodes using patterned diode CNT fabric layers describedfurther above with respect to structure, fabrication, and operation.Carbon-based diode 490 illustrated in FIG. 4H is formed as a PN diodeusing patterned diode CNT fabric layers also described further abovewith respect to structure, fabrication, and operation.

Referring to carbon-based diodes 570 and 580 illustrated in FIGS. 5E and5F, respectively, carbon-based diodes 570 and 580 are formed asSchottky-type diodes using patterned diode graphitic layers describedfurther above with respect to structure, fabrication, and operation.Carbon-based diode 590 illustrated in FIG. 5G is formed as a PN diodeusing patterned diode graphitic layers also described further above withrespect to structure, fabrication, and operation.

Referring to carbon-based diodes 670 and 680 illustrated in FIGS. 6E and6F, respectively, carbon-based diodes 670 and 680 are formed asSchottky-type diodes using patterned diode buckyball layers describedfurther above with respect to structure, fabrication, and operation.Carbon-based diode 690 illustrated in FIG. 6G is formed as a PN diodeusing patterned diode buckyball layers also described further above withrespect to structure, fabrication, and operation.

Field Programmable Gate Arrays (FPGAs)

FPGAs were invented by Ross Freeman, cofounder of the XilinxCorporation, in 1984 to overcome the limitations of array logic, such asXP-PAL 4200 illustrated in FIG. 42. FPGA architectures are dominated byinterconnects. FPGAs are therefore much more flexible in terms of therange of designs that can be implemented and logic functions in themillions and tens of millions and eventually in the hundreds of millionsof equivalent logic gates may be realized. In addition, the addedflexibility enables inclusion of higher-level embedded functions suchadders, multipliers, CPUs, and embedded memory. FPGA architecture andcircuit implementations are described in U.S. Pat. No. Re. 34,363 toFreeman filed on Jun. 24, 1991, and SRAM memory controlled routingswitch circuit implementations are described in U.S. Pat. No. 4,670,749to Freeman filed on Apr. 13, 1984, the contents of which areincorporated herein by reference in their entirety. FPGA 4400 (as shownin FIG. 44) schematically illustrates basic concepts taught by Freemanin the above referenced patents by Freeman. In this application, SRAMcontrol is replaced by control using nonvolatile CNT-based,graphitic-based, and/or buckyball-based electrical functions asdescribed further below.

Referring now to FIG. 44, FPGA 4400 includes an array of configurable(programmable) logic blocks (CLBs) such as CLB 4410 and programmableswitch matrices (PSMs) such as PSM 4420. Interconnections between CLBsand PSMs may be relatively short to provide local wiring (such asinterconnect 4430) or relatively long to provide global wiring (notshown). Input/output (I/O) signal buses, typically with multiple linesper bus, are also shown in FIG. 44.

A programmable switch matrix PSM 4450 interconnecting four CLB blocksCLB1, CLB2, CLB3, and CLB4 is illustrated in FIG. 44. In this example,PSM 4450 may be formed using cross point array 4000 illustrated in FIG.40 and used to interconnect CLB1, CLB2, CLB3, and CLB4 in variouscombinations as illustrated with respect to FIGS. 45A-45D. Nonvolatilecross point switches may be formed with NV CNT resistive block switches130-1, 130-2, 130-3, and 130-4 as illustrated in FIGS. 1B and 1C.However, these NV cross point switches may also be formed with NVgraphitic resistive block switch 162 illustrated in FIG. 1D, or NVbuckyball resistive block switch 182 illustrated in FIG. 1E.

In the PSM 4450 configuration examples that follow, referring to FIG.40, CLB1 is connected to top wire 128, CLB2 is connected to bottom wire122, CLB3 is connected to top wire 126, and CLB4 is connected to bottomwire 124. There are no interconnections between CLB1, CLB2, CLB3, andCLB4 when all cross point arrays are a high resistance OFF state asillustrated in FIG. 40.

Referring to FIGS. 41A-41D, NV cross point switches in a low resistanceON state is shown by a dark circle at the intersection of a top wire anda bottom wire. With respect to configured cross point array 4100, CLB1and CLB2 are electrically connected; with respect to configured crosspoint array 4120, CLB1 and CLB4 are electrically connected; with respectto configured cross point array 4140, CLB1 and CLB2 are electricallyconnected and CLB3 and CLB4 are also electrically connected; and withrespect to configured cross point array 4160, CLB1 and both CLB2 andCLB4 are electrically connected. Other electrically interconnected CLBcombinations may be formed as well.

CLBs may be formed by combining look up tables (LUTs), formed with NRAMin this example, with flip flops and multiplexers as illustratedschematically by CLB 4700 in FIG. 47 and described further below.Alternatively, CLBs may be formed by combining combinatorial logic withflip flops and multiplexers as illustrated by CLB 4600 in FIG. 46, asdescribed further below.

Referring to FIG. 45A, an embodiment of configurable NV select circuit4500 is shown, which is formed using NV CNT switch 4505 and NV CNTswitch 4510 with a first terminal sharing a common node referred to asselect node 4520. Terminals T1 and T2 are connected to a second terminalof NV CNT switches 4505 and 4510, respectively. FET 4515 has a diffusionconnected to select node 4520 and the other diffusion connected to areference such as ground as described in U.S. Pat. No. 7,852,114.Configurable NV select circuits 4500 is a general purpose configurationcircuit and may be used to configure a programmable switch matrix (PSM)and also to configure a configurable logic block (CLB).

Configurable NV select circuit 4500 is described with respect to NV CNTswitches 4505 and 4510 that correspond to NV CNT resistive block switch142 illustrated in FIG. 1C. However, NV CNT switches 4505 and 4510 maybe formed instead with NV graphitic resistive block switch 162illustrated in FIG. 1E, or may be formed instead with NV buckyballresistive block switch 182 illustrated in FIG. 1D.

In operation, when a logic function is programmed, FET 4515 is activated(ON) during write SET (low resistance) or write RESET (high resistance)operations by applying a high voltage to gate G of FET 4515 with programline Y, select node 4520 is connected to a reference voltage such asground and provides a current path between program line X1 and groundand program line X2 and ground through NV CNT switches 4505 and 4510,respectively. Combinations of SET and RESET operations are used to setresistance states (values) of NV CNT switches 4505 and 4510. SET andRESET conditions are described further above with respect to FIG. 19.These resistance states (values) remain nonvolatile even after power isremoved or lost. After SET or RESET operations, FET 4515 is in an (OFF)state by applying a low voltage such as ground to gate G of FET 4515with program line Y and select node 4520 is disconnected from ground.Configurable NV select circuit 4500 is now ready to provide a configuredlogic block function operating in a range of voltages that vary as afunction of the technology node; in the <1V to 5V volts for example. Inthe examples that follow, V_(DD)=2.5 V. is used. Note that while NV CNTcircuits are designed to be in-circuit programmed, this does notpreclude programming in sockets, for example, as is done in some oldertechnologies.

Referring to FIG. 45A, during logic operation, after the configurable NVselect circuit 4500 has been written (that is programmed) and is storedin a nonvolatile state by NV CNT switches 4505 and 4510, operatingvoltages are kept sufficiently low, less than 3 volts for example, sothat the resistance states (values) of NV CNT switches 4505 and 4510 arenot changed (disturbed) under NFPGA operation. Leakage currents are keptlow during logic operation by selecting a high resistance value for oneof the NV CNT switches. By way of example, if NV CNT switch 4505 is inhigh resistance state, 1-10 G Ohms for example, and NV CNT switch 4510is in low resistance state, 100 k Ohms for example, and if X1 is at anon-chip voltage of V_(DD)=2.5 volts and X2 is at a reference voltagesuch as ground (zero volts), then select node 4520 voltage will be atapproximately 0 volts and a current in the range of 250 pA to 2.5 nAflows, but only during logic operation, and only in selected regions ofswitch to keep DC power dissipation low. However, if switch NV CNTswitch 4505 is in a low resistance state, 100 k Ohm for example, and NVCNT switch 4510 is in a high resistance state, 1-10 G Ohms for example,then select node 4520 voltage will be at 2.5 volts and a current in therange of 250 pA to 2.5 nA flows, but only during logic operation, andonly in selected regions of switch to keep DC power dissipation low. FET4515 is OFF during logic operations.

As described further above, FPGA architectures are dominated byprogrammable interconnects, such as programmable switch matrix PSM 4450illustrated in FIG. 44. Referring to FIG. 45B, instead of usingconfigurable cross point arrays in PSM 4450 as described further abovewith respect to FIGS. 40, 41, and 44, CLBs may instead be interconnectedby combining configurable NV select circuit 4500 and FET transfer device4530 to form configurable NV routing circuit 4540 illustrated in FIG.45B.

FIG. 45B illustrates NV routing circuit 4540 in which configurable NVselect circuit 4500-1 with select node 4520-1 corresponds toconfigurable NV select circuit 4500, and controls the gate voltage ofFET 4530 transfer device. In operation, FET transfer device 4530connects, or disconnects, pairs of CLBs by forming and un-forming anelectrical path between them, and logic current flows through FETtransfer device 4530. The logic function of programmable NV routingcircuit 4540 is determined as described further above with respect toconfigurable NV select circuits 4500 and retains the programmed logicfunction even if power is removed or lost.

In operation, select node 4520-1 turns FET 4530 ON if it is at a highvoltage such as 2.5 volts and turns FET 4530 OFF if is at a low voltagesuch as ground. When FET 4530 is ON, signal flow, voltage distribution,current distribution, and power distribution are enabled; and when FET4530 is in an OFF state, then transmission of these functions isdisabled. Multiple configurable NV routing circuits 4540 may be used toform PSM 4450 illustrated in FIG. 44 that forms and un-forms electricalconnections between CLBs.

FIG. 45C illustrates configurable diode-resistor logic AND circuit 4550in which configurable NV select circuit 4500-2 with select node 4520-2may configure or reconfigure the logic function of configurablediode-resistor logic (DRL) AND circuit 4550. Configurable DRL ANDcircuit 4550 is a configurable combinatorial logic circuit and may beused in configurable logic block (CLB) 4600 illustrated in FIG. 46 forexample. DRL AND circuits are described further above with respect toFIG. 43B. Configurable NV select circuit 4500-2 with select node 4520-2corresponds to configurable NV select circuit 4500 and select node 4520,respectively, described further above with respect to FIG. 45A. Selectnode 4520-2 controls an input voltage IN3 to the cathode of diode 4555of DRL NAND gate 4560. The logic function of configurable DRL ANDcircuit 4550 is determined by input IN3 as described in logic functiontable 4570. Configurable DRL AND circuit 4550 retains the programmedlogic function shown in logic function table 4570 even if power isremoved or lost.

In operation, if IN3 is at a low voltage L, near zero volts for example,output O at node 4565 remains near zero volts L regardless of thevoltage values (low voltage L or high voltage H) of input voltages N1and IN2. However, if IN3 is at a high voltage H, such as 2.5 V. forexample, then output O at node 4565 depends on the values of IN1 andIN2. Both IN1 and IN2 need to be at a high voltage H in order for outputO at node 4565 to be at a high voltage H as shown by Boolean logicequation O=IN1·IN2 in logic function table 4570. If either IN1 or IN2,or both IN1 and IN2 are at a low voltage L, then output O is at lowvoltage L.

FIG. 45D illustrates configurable diode-resistor logic OR circuit 4575in which configurable NV select circuit 4500-3 with select node 4520-3may configure or reconfigure the logic function of configurablediode-resistor logic (DRL) OR circuit 4575. Configurable DRL OR circuit4575 is a configurable combinatorial logic circuit and may be used inconfigurable logic blocks (CLBs). DRL OR circuits are described furtherabove with respect to FIG. 43A. Configurable NV select circuit 4500-3with select node 4520-3 corresponds to configurable NV select circuit4500 and select node 4520, respectively, described further above withrespect to FIG. 45A. Select node 4520-3 controls an input voltage IN3 tothe anode of diode 4580 of DRL OR gate 4585. The logic function ofconfigurable DRL OR circuit 4575 is determined by input IN3 as describedin logic function table 4595. Configurable DRL OR circuit 4575 retainsthe programmed logic function shown in logic function table 4595 even ifpower is removed or lost.

In operation, if IN3 is at a high voltage H, approximately 2.5 V forexample, output O at node 4590 remains at a high voltage H regardless ofthe voltage values (low voltage L or high voltage H) of input voltagesIN1 and IN2. However, if IN3 is at a low voltage L, such asapproximately zero volts, for example, then output O at node 4590depends on the values of IN1 and IN2. If either IN1 or IN2, or both IN1and IN2, are at high voltage H, then O at node 4590 is at a high voltageH as shown by Boolean logic equation O=IN1+IN2 in logic function table4595. If both IN1 and IN2 are at a low voltage L, then output O is atlow voltage L.

Referring to FIG. 45A, the embodiment of configurable NV select circuit4500 may be modified to include just one NV CNT switch and one referenceresistor to simplify writing (programming) of the nonvolatile logicstate of the configurable NV select circuit. Modified configurable NVselect circuit 4500 may be formed by replacing NV CNT switch 4510 or NVCNT switch 4505 with a resistor of fixed value. In this example, NV CNTswitch 4510 may be replaced with a resistor of fixed value and NV CNTswitch 4505 may be left unchanged. The resistor may be formed using ametal, metal alloy, conductive oxide, semiconductor, carbon nanotubefabric, or other material. U.S. Pat. No. 7,365,632 describes resistiveelements formed using patterned carbon nanotube fabrics that arecompatible with integration in CMOS processes. Write operations for NVCNT switch 4510 are unchanged.

Referring to the modified configurable NV select circuit describedabove, during logic operation, after the write operation, thenonvolatile NV select circuit state is stored in NV CNT switches 4505.By way of example, if NV CNT switch 4505 is in high resistance state, 1G Ohm for example, and the reference resistor is chosen as 100 k Ohmsfor example, and if X1 is at an on-chip voltage of V_(DD)=2.5 volts andX2 is at a reference voltage such as ground (zero volts), then theselect node voltage will be at approximately 0 volts and a current inthe range of and 2.5 nA flows, but only during logic operation, and onlyin selected regions of switch to keep DC power dissipation low. However,if switch NV CNT switch 4505 is in a low resistance state, 10 k Ohms forexample, then the select node voltage will be at 2.5 volts and a currentof 25 nA flows, determined by the 100 kOhm reference resistor, but onlyduring logic operation, and only in selected regions of switch to keepDC power dissipation low. FET 4515 is OFF during logic operations.

Configurable NV select circuit operation may optionally be enhanced byadding a capacitor between node 4520 (FIG. 45A) and a reference voltagesuch as ground. And this capacitor may also be added to nodes 4520-1,4520-2, and 4520-3 illustrated in FIGS. 45B, 45C, and 45D, respectively,as well as to the modified configurable NV select circuit definedfurther above. Combined with high resistance NV CNT switch resistancevalues, a capacitance of 10's of pF results in a time constant in the10's of microseconds to enhance logic stability of configurable NVselect circuits. For example, as 2.5 Volt signals flow between sourceand drain of the controlled MOSFET, such as MOSFET 4530 illustrated inFIG. 45B, signals coupled to the controlled gate connected to selectnode 4520-1 could not disturb the NV logic state set by the configurableNV select circuit 4500. When writing configurable NV select circuit4500, the mode select MOSFET 4515 is ON and the capacitance is shortedto ground, so no write delays are introduced.

While a V_(DD) of 2.5 volts has been used in these examples,configurable NV select circuits are compatible with V_(DD)=1V and V_(DD)values of less than 1 Volt.

Referring to FIG. 46, configurable logic block (CLB) 4600 may be formedwith configurable combinatorial logic 4610, clocked D flip-flop 4640,and multiplexer (MUX) 4650. In this example, configurable combinatoriallogic 4610 is formed using configurable diode-resistor logic (DRL) ANDcircuit 4550 described further above with respect to FIG. 45C, whoseoutput O is connected to input 4630 of clocked D flip-flop 4640 andinput 4635 of MUX 4650. Output 4645 of D flip-flop 4640 is connected toa second input of MUX 4650.

In operation, configurable combinatorial logic 4610, formed withconfigurable DRL AND circuit 4550, may be configured (programmed) withprogram lines X1, X2, and Y as described further above with respectFIGS. 45C and 45A. When configured, output O corresponds to inputs IN1and IN2 and the programmed state of IN3, as described further above withrespect to logic function table 4570 shown in FIG. 45C. Clocked Dflip-flop latches output O, and MUX 4650 generates output OUT of CLB4600 based on inputs IN1 and IN2 and the configured state of IN3.

While CLB 4600 is illustrated as a having two inputs IN1 and IN2,multiple inputs in excess of two may be used. Also, other circuits maybe used for configurable combinatorial logic 4610, such as using DRL ORgate 4585 illustrated in FIG. 45D. CLB 4600 may be used for one orseveral of the CLBs in FPGA 4400 illustrated in FIG. 44.

Configurable logic block (CLB) 4700 may be formed with configurablelook-up-table (LUT) 4710, clocked D flip-flop 4740, and multiplexer(MUX) 4750 as illustrated in FIG. 47. In this example, configurable LUT4710 is formed using cross point array 4715, corresponding to crosspoint array 2300, with 1-RS cell 2350 or 1-RS cell 2380, describedfurther above with respect to FIGS. 23A, 23B, and 23C, respectively.Word decoder drivers 4720 with inputs IN1, IN2, and IN3, and bit decoderand driver, latch and I/O functions 4725 with inputs IN4 and IN5 may beused to configure (program) cross point array 4715 which contains theconfigurable look-up-table. Output O of bit decoder and driver, latchand I/O functions 4725 is connected to input 4730 of clocked D flip-flop4740 and input 4735 of MUX 4750. Output 4745 of D flip-flop 4640 isconnected to a second input of MUX 4650.

In operation, configurable LUT 4710 may be configured (programmed) withprogram inputs IN1, IN2, IN3, IN4, and IN5 as described further abovewith respect FIGS. 23A, B, and C. And also, as described withprogrammable/reprogrammable AND array 4205, which is used as a crosspoint memory array and corresponding memory mode word decoders WLdrivers 4215 and memory mode bit decode & BL drivers, latch, and I/O4220, when configuration controller 4202 is in memory mode, asillustrated in FIG. 42. When configured, output O corresponds tononvolatile programmed states in cross point array 4715. Clocked Dflip-flop latch 4740 stores output O and MUX 4750 generates output OUTof CLB 4700 based on stored configurable (LUT) 4710 values.

While CLB 4700 is illustrated as a having five inputs used to configurecross point array 4715, multiple inputs less than or in excess of fivemay be used. CLB 4700 may be used for one or several of the CLBs in FPGA4400 illustrated in FIG. 44.

While configurable LUT 4710 was described in terms above with respect tothe AND array subset programmable/reprogrammable AND array 4205illustrated in FIG. 42, CLB 4700 may also be generated using the entireXP-PAL 4200 programmable logic function described further above withrespect to FIG. 42. In this approach, XP-PAL 4200 replaces configurableLUT 4710; logic inputs A, A_(C), B, and B_(C); replace program inputsIN1, IN2, IN3, IN4, and IN5; D flip flops 4260 and 4265 replace D flipflop 4740 and MUX 4750 and corresponding interconnections, and D flipflops 4260 and 4265 provide outputs O1 and O2, respectively.

At this point in the specification, the description of FPGA 4400illustrated in FIG. 44 is complete. However, electrostatic discharge(ESD) protection of interface such as inputs, outputs, and input/outputsconnected to external pads and pins needs to be provided as described inthe referenced book H. B. Bakoglu, “Circuits, Interconnections, andPackaging for VLSI,” Addison-Wesley Publishing Company, 1990, pages46-51. ESD protection of chips using carbon nanotube-based devices isalso described in U.S. Pat. No. 7,839,615, the contents of which areincorporated herein in their entirety by reference.

ESD Protect Circuits

Referring to FIG. 48, ESD protect circuit 4800 may be used to provideelectrostatic discharge protection for FPGA 4400 illustrated in FIG. 44.ESD protect circuit 4800 includes protect diodes PD 4800 and PD 4815 inseries, with the anode of PD 4810 connected to the cathode of PD 4815 atnode 4825. Node 4825 is connected to input/output (I/O) terminal 4830that carries input, output, or input/output signals to and from FPGA4400 illustrated in FIG. 44. Protected circuits 4827 are connected tonode 4825, and to power supply bus 4842 and ground bus 4852 (power andground connections not shown in the drawing). The cathode of PD 4810 isconnected to node 4835 which is connected to terminal 4840 that is usedto supply voltage to power supply bus 4842 as part of FPGA 4400 (notshown in FIG. 44) and the anode of PD 4815 is connected to node 4845which is connected to terminal 4850 that is to used to provide areference voltage such as ground to ground bus 4852 as part of FPGA 4400(not shown in FIG. 44). The series combination of PD 4810 and PD 4815form protective diode pair 4820.

Protective diode pair 4820 may be integrated in chips at any processlevel in the chip fabrication process. Chip level includes analog anddigital chips, and highly integrated chip functions such assystem-on-chip (SoC). In addition to chip level, however, protectivediode pairs 4820 may be formed at various other levels of assembly. Forexample, protective diode pairs 4820 may be formed on a modulesubstrate. Protective diode pairs 4820 may be formed at the card levelor board level as well. Protective diode pairs may be included inmultiple assembly levels such as chip level, module level, card level,and board level to maximize the amount of ESD protection.

Power supply bus 4842 and ground bus 4852 typically have largedecoupling capacitance values. ESD surges are in the nanosecond rangeand the high decoupling capacitance holds power supply bus 4842 and 4852at nearly the same voltage during the ESD surge duration. Focusing onESD protection with respect to circuits 4827 connected to I/O terminal4830, protective diode pair 4820 provides protection in both thepositive and negative voltage surge direction. That is, a positive ESDsurge with respect to terminal 4830, and any other terminal, results inthe corresponding surge current to flow in PD 4810. However, a negativeESD surge with respect to terminal 4830, and any other terminal, resultsin a corresponding surge current to flow in PD 4815.

PD 4810 and PD 4815 have typically been formed of semiconductormaterials such as silicon and gallium arsenide for example. However,carbon-based diodes have high current carrying capacity which may beused for ESD protection. Also, these diodes may be formed at any pointin the fabrication cycle because they do not require a semiconductorsubstrate. In this example, carbon-based diode materials are used toform PD 4810 and PD 4815. These carbon-based protective devices areformed with diode CNT fabric layers, diode graphitic layers, and/ordiode buckyball layers described in detail further above with respect toFIGS. 4F-4H, 5E-5G, and 6E-6G, respectively. Structures, fabrication,and operation are described for various carbon-based diode examplesillustrated in FIGS. 4F-4H, 5E-5G, and 6E-6G.

Referring to carbon-based diodes 470 and 480 illustrated in FIGS. 4F and4G, respectively, carbon-based diodes 470 and 480 are formed asSchottky-type diodes using patterned diode CNT fabric layers describedfurther above with respect to structure, fabrication, and operation.Carbon-based diode 490 illustrated in FIG. 4H is formed as a pn diodeusing patterned diode CNT fabric layers also described further abovewith respect to structure, fabrication, and operation.

Referring to carbon-based diodes 570 and 580 illustrated in FIGS. 5E and5F, respectively, carbon-based diodes 570 and 580 are formed asSchottky-type diodes using patterned diode graphitic layers describedfurther above with respect to structure, fabrication, and operation.Carbon-based diode 590 illustrated in FIG. 5G is formed as a pn diodeusing patterned diode graphitic layers also described further above withrespect to structure, fabrication, and operation.

Referring to carbon-based diodes 670 and 680 illustrated in FIGS. 6E and6F, respectively, carbon-based diodes 670 and 680 are formed asSchottky-type diodes using patterned diode buckyball layers describedfurther above with respect to structure, fabrication, and operation.Carbon-based diode 690 illustrated in FIG. 6G is formed as a pn diodeusing patterned diode buckyball layers also described further above withrespect to structure, fabrication, and operation.

The geometry of the carbon-based diodes described further above arerelatively large to be able to support maximum ESD surge currents in therange of 100 mA to 1 A for example, without exceeding a maximum allowedvoltage across devices in the chip. In this example, if the maximumtolerable voltage for devices in FPGA 4400 is 4 volts, then thedimensions of patterned diode CNT fabric layers 470, 480, and 490 arechosen to prevent a voltage surge of greater than 4 volts for a maximumcurrent surge value between 100 mA and 1 A as required; if the maximumtolerable voltage for devices in FPGA 4400 is 4 volts, then thedimensions of patterned diode graphitic layers 570, 580, and 590 arechosen to prevent a voltage surge of greater than 4 volts for a maximumcurrent surge value between 100 mA and 1 A as required; and if themaximum tolerable voltage for devices in FPGA 4400 is 4 volts, then thedimensions of patterned diode buckyball layers 670, 680, and 690 arechosen to prevent a voltage surge of greater than 4 volts for a maximumcurrent surge value between 100 mA and 1 A as required.

In operation, FPGA 4400 illustrated in FIG. 44 may have power supply bus4842 at 2.5 volts and ground bus 4852 at ground voltage. Input, output,and input/output (I/O) voltage swings are between ground and 2.5 volts.However, signal overshoots and undershoots may occur during operation.Assuming PD 4810 and PD 4815 have forward voltage drops V_(D)=0.5 volts,then no current flows in PD 4810 and PD 4015 for overshoots andundershoots, respectively, of 0.5 V. Therefore, the voltage on terminal4830 may swing between −0.5 V. and +3.0 V without inducing forwardcurrent flow in PD 4810 and 4820.

Voltage Scaling of Dense Memory Arrays

Memory cells and corresponding arrays described further above illustratemethods and corresponding structures for achieving dimensional scalingof cells and corresponding memory arrays to sub-15 nm technology nodesusing integrated diode-resistive change memory arrays. Such memoryarrays can approach densities of 4F². However, there are applicationswhere memory arrays formed with cells using MOSFET select devices and NVCNT resistive block switches may be integrated with cell densitiesapproaching 6F² that are also compatible with nanosecond READ and WRITEoperating speeds. 6F² cell densities can be achieved by optimizingarchitectures and modes of operation that enable MOSFET select devicesto be scaled to small dimensions with corresponding operating voltagesof 1 volt, and yet compatible with NV CNT resistive block switches withSET voltages of 2 volts and RESET voltage of 3 volts as describedfurther below. MOSFET device voltage scaling is required in order toachieve scaled cells at sub-15 nm technology nodes.

Voltage Scaling of NRAM Memories with Diode Select Devices

Referring to FIGS. 4A and 4B, FIGS. 5A-5D, and FIGS. 6A-6D, theformation of various scalable integrated diode-resistive change memoryelements is described further above. Scaling CNT fabric density isillustrated with respect to FIGS. 12A and 12B. Forming doped and undopeddiode nanotube fabric layers, adjusting electrical characteristics byselecting compatible work functions, and other methods, have also beendescribed further above. High density cross point cell areas approaching4F² may be achieved using these methods. In some applications, memoryarchitectures can be optimized to achieved memory arrays with cell areasapproaching 6F² with cells using MOSFET select devices as describedfurther below.

Voltage Scaling of NRAM Memories with MOSFET Select Devices

Referring to FIG. 1A, NV resistive memory cell 100 shows a MOSFET selectdevice 102 in series electrical connection with a NV CNT resistive blockswitch 104. Resistive memory cell 100 is a hybrid technology cell formedby adding NV CNT resistive block switches 104 to an underlying CMOStechnology, which is used for select device 102 in NV resistive memorycells 100 as well as CMOS on-pitch array drivers and other circuits usedto form a memory function. A first conductive terminal 106 of NV CNTresistive block switch 104 is electrically connected to the source S ofMOSFET select device 102 and a second conductive terminal 110 isconnected to array select line SL. Switch nanotube block 108 providesthe nonvolatile storage function in the form of multiple nonvolatileresistance states. Array bit line BL is connected to MOSFET selectdevice 102 drain D. Array word line WL, a portion of which forms thegate of MOSFET select device 102, is used to turn MOSFET select device1020N to form an electrical conducting channel between drain D andsource S, or to turn MOSFET select device 102 OFF to unform theelectrical channel. Bit lines BL and word lines WL are alwaysapproximately orthogonal. Select lines SL may be approximately parallelto bit lines BL in a first architecture or SL may be approximatelyparallel to word lines WL in a second architecture.

NV CNT resistive block switches 104 have been fabricated over a widerange of dimensions, from 200×200 nm to 45 nm, for example. And,referring to FIGS. 3D and 3E, NV CNT resistive block switches 104 havebeen scaled to even smaller dimensions as illustrated by electricallyoperational NV CNT resistive block switch 370, which includes switchnanotube block 372 having dimensions of 15×15 nm. These switches can bescaled to even smaller sub-10 nm dimensions.

CMOS technologies in fabricators around the world operate at 150-200 nmtechnology nodes with MOSFET device voltages of 5.0 Volts for oldertechnologies for example; other technologies operate in the range of35-45 nm with MOSFET device voltages in the range of 2.5-3.3 Volts forexample; and the most advanced fabricators operate at 15-20 nmtechnology nodes with MOSFET voltages in the range of 1-2 Volts forexample. As CMOS technology is scaled to small dimensions, operatingvoltages are scaled to prevent electrical breakdown between source anddrain, prevent breakdown between drain and substrate, and to preventgate oxide failure in the corresponding scaled thin gate oxides. TheseCMOS technology nodes include multiple NMOS and PMOS devices optimizedto several voltages. It is desirable to use the lowest MOSFET device inNV memory cells to achieve the smallest cell area, with higher voltagedevices in on-pitch driver circuits and other memory circuits as needed.

NV CNT resistive block switch 104, fabricated/positioned above MOSFETselect device 102 as shown schematically in FIG. 1A, enables efficientcell layout configurations for both first and second arrayarchitectures. NV CNT resistive block switches 104 may operate invarious modes, bidirectional or unidirectional modes for example, asillustrated in FIG. 20. Furthermore, various memory array and sub-arrayoperating modes may be selected. For example, one or more random bitsalong a word line row may be selected. Alternatively, a sub-block ofbits along multiple word lines may be selected.

As indicated in FIG. 18, nanosecond READ and WRITE speeds are desirable.Referring to FIG. 19, 20 ns READ and WRITE operations were achieved asmeasured on a 4 Mbit NRAM memory configured as a first architecture,with select lines SL parallel to bit lines BL. READ operations areperformed at 1 volt and are therefore compatible with 1 Volt MOSFETdevices. However, in the example illustrated in FIG. 19, the SET (WRITE)operation was performed at 2.5 Volts and the RESET (WRITE) operation wasperformed at 3.5 Volts. Measurements on millions of NV CNT resistiveblock switches 104 show SET voltages in a range of 2-4 volts and RESETvoltages in a range of 3-5 volts.

Referring to FIG. 1A, it is desirable to scale NV CNT resistive blockswitches 104 over a wide range of dimensions, compatible with variousembedded and stand alone NV resistive memory sizes, integrated with thevarious available CMOS technologies from 150 nm to sub-15 nm technologynodes, and compatible with the corresponding MOSFET select device 102operating voltage constraints.

What is needed for the densest NV resistive memories is a combinationof: NV resistive memory architectures and operating modes that enable NVresistive memories, formed with arrays of scaled NV resistive memorycells 100 illustrated in FIG. 1A, operating at 20 ns READ and WRITEspeeds; and NV CNT resistive block switches 104 scaled to small sub-20nm dimensions and operating with SET and RESET voltage of 2V and 3V,respectively, with MOSFET select devices 102 of sub-20 nm dimensionsoperating at 1 volt.

FIGS. 49-57 described further below, illustrate various combinations ofarchitectures and operating modes for NV resistive memories that meetthe voltage scaling conditions described further above that are neededto enable cell dimensional scaling without MOSFET operating voltagelimitations (constraints). FIGS. 49 and 51 illustrate memory sub-arrayschematics 4900 and 5100, respectively, corresponding to a firstarchitecture (SLs parallel to BLs) and a second architecture (SLsparallel to WLs), respectively. FIGS. 50A, 50B, 50C, and 50D illustratethe first architecture memory sub-array schematics 5000, 5020, 5040, and5060, respectively, in various modes of operation. FIGS. 52A, 52B, 52C,and 52D illustrated the second architecture memory sub-array schematics5200, 5220, 5240, and 5260, respectively, in various modes of operation.Tables 5300, 5400, and 5450 illustrated in FIGS. 53, 54A, and 54B,respectively, show voltages across gate oxides, between source anddrain, and between drain and substrate for MOSFET select devices forboth first and second architectures as a function of mode 1 SET andRESET operation. Tables 5500, 5600, and 5650 illustrated in FIGS. 55,56A, and 56B, respectively, show voltages across gate oxides, betweensource and drain, and between drain and substrate for MOSFET selectdevices for both first and second architectures as a function of mode 2SET and RESET operation. Examples of first and second architectures areshown in Patent Pub. No. US 2010/0001267. Examples of secondarchitecture is also shown in U.S. Pat. No. 7,835,170.

Table 5700 illustrated in FIG. 57 summarizes overall results and showscell select MOFET voltage requirements as a function of first and secondarchitectures and modes 1 and 2 for various SET and RESET operations.Table 5700 shows that a combination of the first architecture and mode 2requires the cell select MOSFET to operate at 2 V. However, acombination of the second architecture and mode 2 enables the cellselect MOSFET to operate at 1 V. For both first and secondarchitectures, SET and RESET voltages of 2V and 3V, respectively, may beapplied across the NV CNT resistive block switch. A 2 volts MOSFET isphysically substantially larger than a 1 V. MOSFET, requiring up to atleast 4× the physical area. Hence, the second architecture is scalableto substantially smaller cell dimensions, and therefore smallerresistive memory array dimensions, than the first architecture forreasons described further below.

Referring to FIGS. 49 and 1A, memory first architecture sub-arrayschematic 4900 illustrates an interconnected sub-set of identical cells00, 01, 10, 11, each cell corresponding to NV resistive memory cell 100illustrated in FIG. 1A. Cell 00 illustrates the MOSFET select device T0source connected to one terminal of two terminal NV CNT resistive blockswitch CNT0. MOSFET select device T0 corresponds to MOSFET select device102, and NV CNT resistive block switch CNT0 corresponds to NV CNTresistive block switch 104, with one terminal connected to source S ofMOSFET select device 102. Memory first architecture sub-array schematic4900 is formed by interconnecting word line WL(0) to the gates of MOSFETselect devices T0 and T1, and to other MOSFET gates not shown. Word lineWL(1) is connected to the gates of MOSFET select devices T2 and T3, andto other MOSFET gates not shown. Bit line BL(0) is connected to thedrains of MOSFET select devices T0 and T2, and other drains not shown.Bit line BL(1) is connected to the drains of MOSFET devices T1 and T3and other drains not shown. Select line SL(0), parallel to bit linesBL(0) and BL(1), is connected to the second terminal of NV CNT resistiveblock switches CNT0 and CNT2, and other NV CNT resistive block switchesnot shown. Select line SL(1), parallel to bit lines BL(0) and BL(1), isconnected to the second terminal of NV CNT resistive block switches CNT1and CNT3 and other NV CNT resistive block switches not shown. Theoperation of memory first architecture sub-array schematic 4900 isdescribed further below with respect to FIGS. 50A-50D.

FIG. 50A corresponds to memory first architecture sub-array schematic4900 and illustrates memory first architecture operating mode 5000.Operating mode 5000 corresponds to a random RESET operation in whichone, several, or all bits along a word line row may be RESET. Inoperation, the random RESET may use a first operating mode, mode 1, or asecond operating mode, mode 2. Mode 1 and mode 2 both apply a RESETvoltage V_(RST) across selected NV CNT resistive block switches. In thisexample, cell 00 is selected and V_(RST) is applied across CNT0. In mode1, all voltages are >=0 and bit line and select line voltage maytransition between 0V. and V_(RST) as needed. However, in mode 2, onlyword line voltages are >=0. Bit line and select line voltages maytransition between −V_(RST)/2 and +V_(RST)/2 voltages as needed. For thefirst architecture, mode 2 reduces the voltage across the MOSFET gateoxide and between drain and substrate from V_(SRT) to V_(RST)/2.However, the drain-to-source voltage remains V_(RST) for both mode 1 andmode 2. The highest voltage stress conditions occur in cell 10, with T2OFF.

Use of + and 1 voltages is well known in the industry, especially withrespect to flash technology and analog circuit technology. Typicallyadditional wells are integrated in the process to prevent forwardbiasing of junctions as needed.

FIG. 50B corresponds to memory first architecture sub-array schematic4900 and illustrates memory first architecture operating mode 5020.Operating mode 5020 corresponds to a sub-block RESET operation in whichall bits along word line rows in the sub-block may be RESET. Inoperation, the sub-block RESET may use a first operating mode, mode 1,or a second operating mode, mode 2. Mode 1 and mode 2 both apply a RESETvoltage V_(RST) across selected NV CNT resistive block switches. In thisexample, all cells 00, 01, 10, 11 are selected and V_(RST) is appliedacross CNT0, CNT1, CNT2, and CNT3, respectively. In mode 1, all voltagesare >=0 and bit line and select line voltage may transition between 0V.and V_(RST) as needed. However, in mode 2, only word line voltagesare >=0. Bit line and select line voltages may transition between−V_(RST)/2 and +V_(RST)/2 voltages as needed. Voltage stress conditionsare low across all MOSFET transistors T0, T1, T2, and T3 because theyare all ON as illustrated FIG. 50B.

FIG. 50C corresponds to memory first architecture sub-array schematic4900 and illustrates memory first architecture operating mode 5040.Operating mode 5040 corresponds to a random SET operation in which one,several, or all bits along a word line row may be SET. In operation, therandom SET may use a first operating mode, mode 1, or a second operatingmode, mode 2. Mode 1 and mode 2 both apply a SET voltage V_(SET) acrossselected NV CNT resistive block switches. In this example, cell 00 isselected and V_(SET) is applied across CNT0. In mode 1, all voltagesare >=0 and bit line and select line voltage may transition between 0V.and V_(SET) as needed. However, in mode 2, only word line voltagesare >=0. Bit line and select line voltages may transition between−V_(SET)/2 and +V_(SET)/2 voltages as needed. For the firstarchitecture, mode 2 reduces the voltage across the MOSFET gate oxideand between drain and substrate from approximately V_(SET) to V_(SET)/2.However, the drain-to-source voltage remains V_(SET) for both mode 1 andmode 2. The highest voltage stress conditions occur in cell 10, with T2OFF. However, high voltage can also occur across the gate oxide in Cell01 in mode 1.

FIG. 50D corresponds to memory first architecture sub-array schematic4900 and illustrates memory first architecture operating mode 5060.Operating mode 5060 corresponds to a sub-block SET operation in whichall bits along word line rows in the sub-block may be SET. In operation,the sub-block SET may use a first operating mode, mode 1, or a secondoperating mode, mode 2. Mode 1 and mode 2 both apply a SET voltageV_(SET) across selected NV CNT resistive block switches. In thisexample, all cells 00, 01, 10, 11 are selected and V_(SET) may beapplied across CNT0, CNT1, CNT2, and CNT3, respectively, as needed. Inmode 1, all voltages are >=0 and bit line and select line voltage maytransition between 0V. and V_(SET) as needed. However, in mode 2, onlyword line voltages are >=0. Bit line and select line voltages maytransition between −V_(SET)/2 and +V_(SET)/2 voltages as needed. Voltagestress conditions are relatively high only between drain and substrate,but low across gate oxide and between source and drain, for all MOSFETtransistors T0, T1, T2, and T3 because they are all ON as illustratedFIG. 50D.

Referring to FIGS. 51 and 1A, memory second architecture sub-arrayschematic 5100 illustrates an interconnected sub-set of identical cells00, 01, 10, 11, each cell corresponding to NV resistive memory cell 100illustrated in FIG. 1A. Cell 00 illustrates the MOSFET select device T0source connected to one terminal of two terminal NV CNT resistive blockswitch CNT0. MOSFET select device T0 corresponds to MOSFET select device102, and NV CNT resistive block switch CNT0 corresponds to NV CNTresistive block switch 104, with one terminal connected to source S ofMOSFET select device 102. Memory first architecture sub-array schematic5100 is formed by interconnecting word line WL(0) to the gates of MOSFETselect devices T0 and T1, and to other MOSFET gates not shown. Word lineWL(1) is connected to the gates of MOSFET select devices T2 and T3, andto other MOSFET gates not shown. Bit line BL(0) is connected to thedrains of MOSFET select devices T0 and T2, and other drains not shown.Bit line BL(1) is connected to the drains of MOSFET devices T1 and T3,and other drains not shown. Select line SL(0), parallel to word linesWL(0) and WL(1), is connected to the second terminal of NV CNT resistiveblock switches CNT0 and CNT1, and other NV CNT resistive block switchesnot shown. Select line SL(1), parallel to word lines WL(0) and WL(1), isconnected to the second terminal of NV CNT resistive block switches CNT2and CNT3, and other NV CNT resistive block switches not shown. Theoperation of memory first architecture sub-array schematic 5100 isdescribed further below with respect to FIGS. 52A-52D.

FIG. 52A corresponds to memory first architecture sub-array schematic5100 and illustrates memory second architecture operating mode 5200.Operating mode 5200 corresponds to a random RESET operation in whichone, several, or all bits along a word line row may be RESET. Inoperation, the random RESET may use a first operating mode, mode 1, or asecond operating mode, mode 2. Mode 1 and mode 2 both apply a RESETvoltage V_(RST) across selected NV CNT resistive block switches. In thisexample, cell 00 is selected and V_(RST) is applied across CNT0. In mode1, all voltages are >=0 and bit line and select line voltage maytransition between 0V. and V_(RST) as needed. However, in mode 2, onlyword line voltages are >=0. Bit line and select line voltages maytransition between −V_(RST)/2 and +V_(RST)/2 voltages as needed. Thehighest voltage stress conditions occur in cell 10, with T2 OFF, forV_(RST) voltage across the gate oxide and between drain and substrate inmode 1 and V_(RST)/2 in mode 2. However, the voltage betweendrain-and-source is V_(RST)/2 for both mode 1 and mode 2 because thesecond architecture is used. By way of contrast, as described furtherabove with respect to FIG. 50A, the first architecture results in theentire RESET voltage V_(RST) between drain-and-source terminals for bothmode 1 and mode 2.

FIG. 52B corresponds to memory second architecture sub-array schematic5100 and illustrates memory second architecture operating mode 5220.Operating mode 5220 corresponds to a sub-block RESET operation in whichall bits along word line rows in the sub-block may be RESET. Inoperation, the sub-block RESET may use a first operating mode, mode 1,or a second operating mode, mode 2. Mode 1 and mode 2 both apply a RESETvoltage V_(RST) across selected NV CNT resistive block switches. In thisexample, all cells 00, 01, 10, 11 are selected and V_(RST) is appliedacross CNT0, CNT1, CNT2, and CNT3, respectively. In mode 1, all voltagesare >=0 and bit line and select line voltage may transition between 0V.and V_(RST) as needed. However, in mode 2, only word line voltagesare >=0. Bit line and select line voltages may transition between−V_(RST)/2 and +V_(RST)/2 voltages as needed. Voltage stress conditionsare low across all MOSFET transistors T0, T1, T2, and T3 because theyare all ON as illustrated FIG. 50B.

FIG. 52C corresponds to memory second architecture sub-array schematic5100 and illustrates memory second architecture operating mode 5240.Operating mode 5240 corresponds to a random SET operation in which one,several, or all bits along a word line row may be SET. In operation, therandom SET may use a first operating mode, mode 1, or a second operatingmode, mode 2. Mode 1 and mode 2 both apply a SET voltage V_(SET) acrossselected NV CNT resistive block switches. In this example, cell 00 isselected and V_(SET) is applied across CNT0. In mode 1, all voltagesare >=0 and bit line and select line voltage may transition between 0V.and V_(SET) as needed. However, in mode 2, only word line voltagesare >=0. Bit line and select line voltages may transition between−V_(SETT)/2 and +V_(SET)/2 voltages as needed. For the secondarchitecture, mode 2 reduces the voltage across the MOSFET gate oxideand between drain and substrate from approximately V_(SET) to V_(SET)/2.However, the voltage between drain and source is V_(SET)/2 for both mode1 and mode 2 because the second architecture is used. The highestvoltage stress conditions occur in cell 10, with T2 OFF. However, highvoltage can also occur across the gate oxide in Cell 01 in mode 1.

FIG. 52D corresponds to memory second architecture sub-array schematic5100 and illustrates memory second architecture operating mode 5260.Operating mode 5260 corresponds to a sub-block SET operation in whichall bits along word line rows in the sub-block may be SET. In operation,the sub-block SET may use a first operating mode, mode 1, or a secondoperating mode, mode 2. Mode 1 and mode 2 both apply a SET voltageV_(SET) across selected NV CNT resistive block switches. In thisexample, all cells 00, 01, 10, 11 are selected and V_(SET) may beapplied across CNT0, CNT1, CNT2, and CNT3, respectively, as needed. Inmode 1, all voltages are >=0 and bit line and select line voltage maytransition between 0V. and V_(SET) as needed. However, in mode 2, onlyword line voltages are >=0. Bit line and select line voltages maytransition between −V_(SET)/2 and +V_(SET)/2 voltages as needed. Voltagestress conditions are relatively high only between drain and substrate,but low across gate oxide and between source and drain, for all MOSFETtransistors T0, T1, T2, and T3 because they are all ON as illustratedFIG. 50D

Referring to FIG. 53, table 5300 summarizes first architecture andsecond architecture operating conditions for mode 1 for random RESET andrandom SET operations, and for sub-block RESET and sub-block SEToperations. MOSFET select device gate-to-source voltages |V_(GS)|,drain-to-source voltages |V_(SD)|, and drain to substrate voltages|V_(D-SUB)| are shown for both first and second architectures. Absolutevalues are used because both positive and negative polarities may occur.For the random RESET and SET modes, |V_(DS)| values are highlighted bydotted oval 5350 for the second architecture because |V_(DS)| for thesecond architecture are V_(RST)/2 and V_(SET)/2 for random SET and RESEToperations, respectively for mode 1. By way of contrast, for the firstarchitecture, corresponding |V_(DS)| values are V_(RST) and V_(SET),respectively, for mode 1.

Referring to FIG. 54A, table 5400 shows the same table as 5300 but withvoltage values of V_(RST)=3V. and V_(SET)=2 V. In this example, mode 1Arefers to an operating mode in which random SET and RESET operations areperformed. Highlighted gate, source-drain, and drain-substrate voltagesare compared and show that all voltages are the same, except forsource-drain voltage which is lower by a factor of 2 for the secondarchitecture. Both first and second architectures require 3 volt MOSFETselect devices.

Referring to FIG. 54B, table 5450 shows the same table as 5300 but withvoltage values of V_(RST)=3V. and V_(SET)=2 V. Mode 1B refers to anoperating mode in which random SET and sub-block RESET operations areperformed to lower the required voltages. Highlighted gate,source-drain, and drain-substrate voltages show that all voltage are thesame, except for source-drain voltage which is lower by a factor of 2for the second architecture. Both first and second architectures require2 volt MOSFET select devices. In the mode 2B operation, it may bepossible to use the second architecture with a 1.5 volt MOSFET selectdevice for applications with lower reliability requirements.

As discussed further above, the first architecture results in V_(SET)and V_(RST) applied between MOSFET select device source and drain forrandom SET and RESET operations, respectively, for both mode 1 and mode2, while the second architecture results in V_(SET)/2 and V_(RST)/2applied between MOSFET select device source and drain for random SET andRESET operations, respectively, for both mode 1 and mode 2. This 2×difference in MOSFET select device source-drain operating voltages is aconsequence of select lines SL parallel to word lines WLs for the secondarchitecture as illustrated by comparing FIGS. 52A and 50A and FIGS. 52Cand 52C. Because of the SL orientation difference between the first andsecond architecture, the effect of the mode 2 is substantially greaterfor the second architecture as illustrated further below with respect toFIGS. 55, 56A, and 56B.

Referring to FIG. 55, table 5500 summarizes first architecture andsecond architecture operating conditions for mode 2 for random RESET andrandom SET operations, and for sub-block RESET and sub-block SEToperations. MOSFET select device gate-to-source voltages |V_(GS)|,drain-to-source voltages |V_(SD)|, and drain to substrate voltages|V_(D) _(_) _(SUB)| are shown for both first and second architectures.|V_(GS)| and |V_(D) _(_) _(SUB)| are reduced by a factor of 2 for mode 2compared to mode 1 for both first and second architectures. And |V_(DS)|values remain the same for both mode 1 and mode 2. For the random RESETand SET modes, |V_(DS)| values are highlighted by dotted oval 5550 forthe second architecture because |V_(DS)| for the second architecture areV_(RST)/2 and V_(SET)/2 for random SET and RESET operations,respectively for mode 2. By way of contrast, for the first architecture,corresponding |V_(DS)| values are V_(RST) and V_(SET), respectively, formode 2.

Referring to FIG. 56A, table 5600 shows the same table as 5500 but withvoltage values of V_(RST)=3V and V_(SET)=2 V. In this example, mode 2Arefers to an operating mode in which random SET and RESET operations areperformed. Highlighted gate, source-drain, and drain-substrate voltagesare compared and show |V_(GS)| and |V_(D-SUB)| are reduced from 3V to1.5 volts, but that |V_(SD)| remains 3V. for the first architecture. Bycontrast, |V_(GS)| and |V_(D-SUB)| are reduced from 3V to 1.5 volts, andthat |V_(SD)| remains 1.5V. for the second architecture. In a random SETand RESET mode, the first architecture requires a 3 Volt MOSFET device,while the second architecture requires a 1.5 Volt MOSFET device.

Referring to FIG. 56B, table 5650 shows the same table as 5500 but withvoltage values of V_(RST)=3V and V_(SET)=2 V. Mode 2B refers to anoperating mode in which random SET and sub-block RESET operations areperformed to lower the required voltages. Highlighted gate,source-drain, and drain-substrate voltages are compared and show|V_(GS)| and |V_(D-SUB)| are reduced to approximately 1 volt, but that|V_(SD)| is equal to V_(SET) which is 2V for the first architecture. Bycontrast, |V_(GS)| and |V_(D-SUB)| are reduced from approximately 1volts, and that |V_(SD)| is equal to V_(SET)/2 which is 1V. for thesecond architecture. In a random SET and RESET mode, the firstarchitecture requires a 2 Volt MOSFET device, while the secondarchitecture requires a 1 Volt MOSFET device. Highlighted gate,source-drain, and drain-substrate voltages show that all voltage are thesame, except for source-drain voltage which is lower by a factor of 2for the second architecture. The first and second architectures require2 volt and 1 volt MOSFET select devices, respectively.

Table 57 illustrated in FIG. 57 summarizes the voltage requirements ofMOSFET cell select devices. For the first architecture, a 2 volt MOSFETdevice is required for mixed random and sub-block write selectoperation. While for the second architecture, a 1 volt MOSFET device isrequired. In these examples, the SET voltage is V_(SET)=2V and the RESETvoltage is V_(RST)=3 V.

The second architecture has a layout advantage with respect to the firstarchitecture because there are fewer column lines required. FIG. 49shows the first architecture with both SL(0) and BL(1) (two) columnarray wires. FIG. 51 shows the second architecture with BL(1) (one)column array wire. Reducing column array wires enables smaller NVresistive memory cells. The addition of select lines SL parallel to wordlines WL increases the number of rows. However, this increase has almostno effect on NV resistive memory cell area. As describe further above,from both a layout and voltage scaling standpoint, the secondarchitecture may approach NV resistive memory cell densities of 6F².

While first and second architectures and operating modes have beendescribed in terms of NV CNT resistive block switches, the same resultsapply to cells with NV graphitic block switches or NV buckyballresistive block switches. First and second architectures and operatingmodes may also be applied to other resistive memories such as thoseformed with metallic oxide storage elements.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention not be limited by thespecific disclosure herein, but rather be defined by the appendedclaims; and that these claims will encompass modifications of andimprovements to what has been described.

What is claimed:
 1. A diode, comprising: a first multi-layer carbonblock, said first multi-layer carbon block comprising at least twocarbon layers, each carbon layer comprising multiple, interconnectedcarbon structures; and a second multi-layer carbon block, said secondmulti-layer carbon block comprising at least two carbon layers, eachcarbon layer comprising multiple, interconnected carbon structures;wherein said second multi-layer carbon block is in electricalcommunication with said first multi-layer carbon block; wherein saidfirst multi-layer carbon block and said second multi-layer carbon blockcomprise a diode carbon layer; and wherein said diode carbon layerincludes a pn junction between said first multi-layer carbon block andsaid second multi-layer carbon block.
 2. The diode of claim 1, whereinat least one of said first multi-layer carbon block and said secondmulti-layer carbon block is a nanotube fabric.
 3. The diode of claim 2,wherein said nanotube fabric comprises carbon nanotubes.
 4. The diode ofclaim 2, wherein said first multi-layer carbon block is a p-typenanotube fabric and said second multi-layer carbon block is an n-typenanotube fabric.
 5. The diode of claim 1, wherein at least one of saidfirst multi-layer carbon block and said second multi-layer carbon blockis a graphitic block.
 6. The diode of claim 5, wherein said firstmulti-layer carbon block is a p-type graphitic block and said secondmulti-layer carbon block is an n-type graphitic block.
 7. The diode ofclaim 1, wherein at least one of said first multi-layer carbon block andsaid second multi-layer carbon block is a buckyball block.
 8. The diodeof claim 7, wherein said buckyball block comprises BuckminsterfullerenesC₆₀.
 9. The diode of claim 7, wherein said first multi-layer carbonblock is a p-type buckyball block and said second multi-layer carbonblock is an n-type buckyball block.
 10. The diode of claim 1, whereinsaid first multi-layer carbon block is an anode of said diode and saidsecond multi-layer carbon block is a cathode of said diode.
 11. Thediode of claim 1, wherein said conductive path is directional.
 12. Adiode, comprising: a conductive layer; and a multi-layer carbon block,said multi-layer carbon block comprising at least two carbon layers,each carbon layer comprising multiple, interconnected carbon structures;wherein said multi-layer carbon block is in electrical contact with saidconductive layer; wherein said conductive layer and said multi-layercarbon block comprise a diode carbon layer; and wherein said diodecarbon layer includes a Schottky junction between said conductive layerand said multi-layer carbon block.
 13. The diode of claim 12, whereinsaid multi-layer carbon block is a nanotube fabric.
 14. The diode ofclaim 13, wherein said nanotube fabric comprises carbon nanotubes. 15.The diode of claim 13, wherein said multi-layer carbon block is at leastone of a p-type nanotube fabric and an n-type nanotube fabric.
 16. Thediode of claim 12, wherein said multi-layer carbon block is a graphiticblock.
 17. The diode of claim 16, wherein said multi-layer carbon blockis at least one of a p-type graphitic block and an n-type graphiticblock.
 18. The diode of claim 12, wherein said multi-layer carbon layeris a buckyball block.
 19. The diode of claim 18, wherein said buckyballblock comprises Buckminsterfullerenes C₆₀.
 20. The diode of claim 18,wherein said multi-layer carbon block is at least one of a p-typebuckyball block and an n-type buckyball block.
 21. The diode of claim12, wherein said multi-layer carbon block is at least one of an anode ofsaid diode and a cathode of said diode.
 22. The diode of claim 12,wherein said conductive path is directional.